Mapping Mountains – Hill Reclassifications – The 500-Metre Tops of England and Wales – Deweys

ADDED TO THE DEWEY LIST AS BRYN YR ŴYN (SN 839 925) WITH THE HIGHER QUALIFYING HILL NOW SUBSTANTIATED AS ESGAIR GREOLEN (SN 835 920)

Esgair Greolen (SN 835 920) – Dewey addition

This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Deweys and where I have had direct association with the status change.  These posts will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the Mountain tables book.

Esgair Greolen (SN 835 920)

The 500-Metre Tops of England and Wales are affectionately known after their hill list compiler; Michael Dewey.  This list mixes metric and imperial height in its criteria to bookend up to the 2000ft height band and takes in all hills in England, Isle of Man and Wales that are 500m and above and below 2000ft (609.6m) in height that have 30m minimum drop.

This list formed one of a number of lists that appeared in the Mountain tables book published by Constable in 1995 and at the time of publication comprised 373 hills with 164 in England, 5 in the Isle of Man and 204 in Wales.  The Deweys have undergone extensive revision since first publication with the initial stages forming the basis of this revision given below:

1995    Mountain tables published by Constable with 373 hills listed as Deweys.

April 2000    Strider (LDWA quarterly booklet) publishes contact details for David Purchase and Myrddyn Phillips who have found and list 24 and 14 possible new 500m tops respectively.

It was expanded versions of the above two lists that formed the basis of the next publication:

25^th May 2000    List of Possible 500 Metre Tops by Michael Dewey listing 44 hills.

David Purchase expands his Additional Dewey 500m Hills and Myrddyn Phillips produces lists of English 500m hills to measure and Welsh 500m hills to measure.

These lists formed the basis of the next publication:

29^th June 2000    Possible/Probable 500’s by Michael Dewey listing 77 hills.  Michael adopts following protocol; if one person proposes that a top should qualify as a 500 by personal survey, and is then confirmed by a second person, it should then be promoted to the main list.

April 2002    The 500+ Tops of England and Wales – The ‘New Deweys’ published in the Strider booklet and listing 66 new qualifying hills.

25^th May 2006    Rob Woodall republishes Michael’s main and possible/probable lists on the RHB Yahoo group file database. 

 

Mountain tables by Michael Dewey

The details for this addition appear below:

The name the hill is listed by in the Deweys is Esgair Greolen, and it is adjoined to the Pumlumon group of hills which are situated in the central part of Wales, and it is positioned with the A44 road to its south and the B4518 road to its east, and has the town of Machynlleth towards the north-west and Llanidloes towards the south-east.

This hill was not included in the original 1995 Constable publication, but with a small uppermost 500m ring contour and bwlch contouring between 470m – 480m that appear on the Ordnance Survey 1:25,000 Explorer map, this hill was noted as an outside possibility for a potential new Dewey.

Extract from the Ordnance Survey 1:25,000 Explorer map

The above detail was noted by Myrddyn Phillips who then conducted a basic levelling survey (BLS) of this hill on the 11^th July 2000, resulting in 106½ft / 32.5m of drop, with Bryn yr Ŵyn (SN 839 925) surveyed as higher than Esgair Greolen (SN 835 920).  These details were forwarded to the list author; Michael Dewey and the hill was added to the list with the date of survey given in the Remarks column accompanying the list.

Gathering data at the summit of Esgair Greolen

Gathering data at the bwlch of Esgair Greolen

Gathering data at the summit of Bryn yr Ŵyn

As the margin of uncertainty for the BLS method of surveying over terrain such as that on this hill is approximately +/- 2m and as the resulting 32.5m of drop was near the minimum 30m qualifying drop value and as both summits only have a small uppermost 500m ring contour, this hill was prioritised for a GNSS survey, and this took place over two days; on the 5^th and 13^th May 2016.  The summit and bwlch of this hill were surveyed by Myrddyn Phillips using a Trimble GeoXH 6000, resulting in a 501.4m summit height for Esgair Greolen and a 499.9m summit height for Bryn yr Ŵyn and a 471.2m bwlch height, with these values giving Esgair Greolen 30.3m of drop and in the process relocating the qualifying hill to the higher summit and confirming its Dewey status.

The full details for the hill are:

Name:  Esgair Greolen

OS 1:50,000 map:  135, 136

OS 1:25,000 map:  214, 215

Summit Height:  501.4m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 83574 92022 (Trimble GeoXH 6000)

Bwlch Height:  471.2m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SN 83220 91901 (Trimble GeoXH 6000)

Drop:  30.3m (Trimble GeoXH 6000)

Myrddyn Phillips (June 2020)

Mapping Mountains – Significant Name Changes – Y Pellennig - The Remotest Hills of Wales, Welsh Highlands - Uchafion Cymru and 500m Twmpau

Bryn Llwyd (SN 835 920)

There has been a Significant Name Change to a hill that appears in the following listings, Y Pellennig - The Remotest Hills of Wales, Yr Uchafion and the 500m Twmpau, with the height, drop, summit relocation and status of the hill being confirmed by a survey with the Trimble GeoXH 6000 which took place on the 5^th May 2016 and the 13^th May 2016.

The criteria for the three listings that this name change applies to are:

Y Pellennig –The Remotest Hills of Wales comprise all Welsh hills whose summit is 2.5km or more from the nearest paved public road and which have a minimum 15m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams.

Yr Uchafion - All Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams. 

500m Twmpau - All Welsh hills at or above 500m and below 600m in height with 30m minimum drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.  The list is authored by Myrddyn Phillips.  

The hill is a part of the Pumlumon range, which is an extensive group of hills in the north-western part of Mid and West Wales, and it is relatively remote for a Welsh hill with the nearest small community being Penffordd-las (Staylittle) to the east.

The Trimble GeoXH 6000 gathering data at the summit of Bryn Llwyd

The listed summit of this hill has been relocated from Bryn yr Ŵyn at SN 83919 92571 to Bryn Llwyd at SN 83574 92022, with the latter surveyed with the Trimble GeoXH 6000 as being 1.5m higher.  

The hill first made an appearance in a hill list in 1997 when John Kirk listed it as Bryn Yr Wyn, using the name of the adjacent hill but with the correct grid reference in his Kirk’s BIG Mountain List, this list that remains unpublished but available via the author.  The adjacent lower hill was later included by Michael Dewey and listed as Bryn yr Wyn in the April 2002 edition of Strider, which included the updates to The 500-Metre Tops of England and Wales list that appeared in his Mountain tables book published by Constable in 1995.  The summit of the Dewey was later relocated due to the Trimble GeoXH 6000 survey to the higher summit and listed as Esgair Greolen.

Prior to making local place-name enquiries the now known higher summit was accepted as being named Esgair Greolen, and since this summit has usurped its neighbour as being the higher, this is the name used in Michael’s list to The 500-Metre Tops of England and Wales.

Hill list authors are prone to list a hill by the name that appears nearest to its summit on contemporary Ordnance Survey maps, without much consideration for its local or historical confirmation, or whether map placement is appropriate.  However, place-name data can be improved by asking local people and examining historical documents, and on the way to survey this hill for the second time with the Trimble GeoXH 6000 I made place-name enquiries with the local farmer, who kindly took me up in his two seater quad bike toward the hill.  Afterward both Aled and I examined a number of historical maps for evidence of where the name of Esgair Greolen originated and where it is applicable to.

The local farmer I met is named Gareth Griffith and he had farmed from Nant-yr-hafod for forty years, he was out with his dogs heading up the hill to feed the sheep.  As we chatted I asked him about the names of the local hills, and he rolled off name after name of the local hills and streams, one in particular proved extremely interesting, it related to the hill that Ordnance Survey maps name as Esgair Greolen, which was the hill I wanted to concentrate the morning’s surveying activities on.  Gareth knew this hill as Bryn Llwyd, and said that ‘this name doesn’t appear on the map.’  I asked him about the name of Esgair Greolen, and he had never heard of it.

Gareth Griffith

Gareth gave me a lift up the hill on his two seater quad bike and dropped me off at the end of the track close to the forested summit of Fedw Ddu.  From this vantage point we were looking across to Bryn yr Ŵyn and also the hill I planned on prioritising to survey, and Gareth pointed toward each and named them, Bryn yr Ŵyn and Bryn Llwyd, the latter is the hill named as Esgair Greolen on contemporary Ordnance Survey maps.

When back home I examined old Ordnance Survey maps and forwarded the details of my meeting with Gareth Griffith to Aled, who proceeded to research where the name of Esgair Greolen originated and what feature this name may be applicable to.  Aled’s comments relating to this appear in the 2^nd edition of Y Pellennig - The Remotest Hills of Wales, and are reproduced below:

The OS have applied the name Esgair Greolen to this hill since the 1901 Six-Inch map, however earlier OS maps provide conflicting information regarding the positions of the steams named Nant Esgair Greolen and Nant y Barcud, which casts uncertainty over the exact position of Esgair Greolen.  A single local contact failed to confirm Esgair Greolen as the name of this hill, but instead visually identified the hill as being known as Bryn Llwyd.

Extracts from a number of Ordnance Survey maps appear below giving detail relating to the name placement of Esgair Greolen and the steams of Nant Esgair Greolen and Nant y Barcud.

Extract from the Ordnance Survey One-Inch 'Old Series' map

Extract from the 1886 Ordnance Survey Six-Inch map

Extract from the 1903 Ordnance Survey Six-Inch map with the stream previously recorded as Nant y Barcud now recorded as the Nant Esgair Greolen

Extract from the Ordnance Survey 1903 Six-Inch map where the name Esgair Greolen first appeared on an Ordnance Survey map

Extract from the current Ordnance Survey 1:25,000 Explorer map

As a result of this research the hill has subsequently been listed under the name of Bryn Llwyd in Y Pellennig – The Remotest Hills of Wales, Yr Uchafion and the 500m Twmpau, and this name was derived from local enquiry and does not appear on any Ordnance Survey map.

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Pumlumon

Name:  Bryn Llwyd

Previously Listed Name:  Esgair Greolen 

Summit Height:  501.4m (converted to OSGM15 and average of four summit surveys)

OS 1:50,000 map:  135, 136

Summit Grid Reference:  SN 83574 92022 

 

Drop:  30.3m (converted to OSGM15)

For details on the 1^st survey and the 2nd survey of Bryn Llwyd

Myrddyn Phillips and Aled Williams (December 2016)

Mapping Mountains – Hill Reclassifications – Y Pellennig – The Remotest Hills of Wales

Bryn Llwyd (SN 835 920) - Pellennig addition  

There has been a new hill that has entered the list of Y Pellennig – The Remotest Hills of Wales, due to a recent Trimble survey.  The hill is situated in the Pumlumon group of hills in the northern part of mid Wales and is situated between the towns of Llanidloes to its south-east and Machynlleth to its north-west.

The hill was surveyed over two days on 5^th and 13^th May 2016, both in beautiful sunshine and its name is Bryn Llwyd.  It can be accessed from the east via a track that leaves a minor road toward the farm of Nant-yr-hafod, or alternatively it can be accessed from its north via a track that leaves a minor road leading toward the lake of Glaslyn, or from a track that leaves the same minor road and makes its way around the southern flank of Y Grug.  These approaches from the north have to contend with Cors yr Ebolion, which as its Welsh name suggests is a bog.  If tempted by one of these northern approaches it is advisable to keep to a path that contours the eastern flank of Banc Bugeilyn before losing height to cross the reed infested stream close to the south-west corner of the conifer plantation to the north of this hill’s summit.

Bryn Llwyd was surveyed by the Trimble GeoXH 6000 as being 501.4m (converted to OSGM15, and average of four summit surveys) high, and prior to this survey the highest point listed hereabouts was Bryn yr Ŵyn which had been regarded as being higher than Bryn Llwyd and therefore listed as the summit in the 500m Twmpau list.  However, Bryn yr Ŵyn was surveyed by the Trimble as being 499.9m (converted to OSGM15, and average of five summit surveys) high, and as contour interpolation and a rudimentary survey suggested that the connecting bwlch between these two hills was not low enough to give each sufficient drop to be listed as separate summits; only Bryn yr Ŵyn was previously listed.  This Trimble survey confirms Bryn Llwyd to be the higher summit (see Summit Relocation post) and as the nearest paved public road at SN 84696 94288 is 2.525km from the summit this hill qualifies for the listing of Y Pellennig – The Remotest Hills of Wales, having the required 15m minimum drop and 2.5km minimum distance between the summit and the nearest paved public road.

This now brings the overall total for Y Pellennig to 168 hills for the Complete list (All Wales), with the total for the Mainland Wales list being 124 hills.  The Master List will be duly updated on the Mapping Mountains site.

The full details for the hill are:

Cardinal Hill:  Pumlumon Fawr

Summit Height:  501.4m (converted to OSGM15, and average of four summit surveys)

Name:  Bryn Llwyd

OS 1:50,000 map:  135, 136

Summit Grid Reference:  SN 83574 92022

Drop:  30.3m (converted to OSGM15)

Distance:  2.525km

The list of additions and deletions in the Pellennig list since the 1^st edition of Y Pellennig – The Remotest Hills ills of wales of Wales was published by Europeaklist is as follows:

ADDITIONS

Pen Diban (SH 112 205)

Ynys Arw (SH 266 945)

Bryn Llwyd (SN 835 920) 1st survey, 2nd survey

DELETIONS

Graig Fach (SN 821 931)

Bryn Llwyd (SN 835 920) now confirmed as a Pellennig hill

ills of wales For details on the 1st Trimble survey and the 2nd Trimble survey that promoted this hill to Pellennig status.

Myrddyn Phillips and Aled Williams (May 2016)

Mapping Mountains – Summit Relocations – Y Pellennig, Yr Uchafion and 500m Twmpau

Bryn Llwyd (SN 835 920)  

There has been a Summit Relocation initiated by a survey with the Trimble GeoXH 6000 to the listings of Y Pellennig, Yr Uchafion and 500m Twmpau, with the survey that resulted in this summit relocation being conducted on the 5^th and 13^th May 2016.

The three lists that this summit relocation affects are:

Y Pellennig - The Remotest Hills of Wales, with the criteria being all hills in Wales whose summit is 2.5km or more from the nearest paved public road that have a minimum 15m of drop.  This list is co-authored by Myrddyn Phillips and Aled Williams.

Yr Uchafion, this is the working title for a list that takes in all hills in Wales at and above 500m in height that have a minimum 15m of drop.  This list is co-authored by Myrddyn Phillips and Aled Williams.

500m Twmpau (thirty welsh metre prominences and upward), with the criteria being all Welsh hills at or above 500m and below 600m in height that have a minimum 30m of drop.  This list is authored by Myrddyn Phillips.

As the hill only entered the ranks of Pellennig hills due to this survey this listing of hills is being included within this Summit Relocations heading. 

The survey was conducted in the Pumlumon range of hills over two beautiful sunny days, with the hill situated mid-way between the towns of Machynlleth to its north-west and Llanidloes to its south-east.  

The name of the hill where the summit has been re-located to is Bryn Llwyd (SN 835 920) and the name of the hill where the summit has been re-located from is Bryn yr Ŵyn (SN 839 925).  Both summits and respective bylchau were surveyed with the Trimble with their summits being connected by a bwlch that is only 9.9m below the summit height of Bryn yr Ŵyn and 11.4m below the summit height of Bryn Llwyd.

The summits of both hills possess a small uppermost 500m ring contour on Ordnance Survey maps with no adjoined spot height, with the uppermost ring contour for Bryn Llwyd being the larger.

The critical bwlch for the higher of these hills in positioned to the south-west and to my knowledge their drop has only been surveyed on three occasions, once using a basic levelling survey (BLS) method, and the other two using the Trimble GeoXH 6000.  The results from each survey appear below:

Bryn Llwyd:  summit to critical bwlch, 102.5ft (31.2m) drop (BLS), 30.3m drop (Trimble).

Bryn yr Ŵyn:  summit to connecting bwlch with Bryn Llwyd, 42.5ft (13.0m) drop (BLS), 9.9m drop (Trimble).   

I conducted the basic levelling survey in July 2000 and sent the details to Michael Dewey.  Michael assessed the information and decided to include Bryn yr Ŵyn in his list to The 500-Metre Tops of England and Wales.  The margin of uncertainly associated with the BLS method is within the error tolerance of the result, and I have wanted to re-visit and survey both hills and produce accurate absolute heights for each, ever since.  Their heights as surveyed by the Trimble GeoXH 6000 appear below:

Bryn Llwyd 501.4m (converted to OSGM15) summit at SN 83574 92022 (average of four surveys conducted over two days)

Bryn yr Ŵyn 499.9m (converted to OSGM15) summit at SN 83919 92571 (average of five surveys conducted over two days)

Therefore the position of the relocated summit is at SN 83574 92022 and it consists of grass atop an ancient mound.  The summit area and the hill itself has relatively easy underfoot conditions and consists of moor grass with a path leading from the critical bwlch to the south-west toward the connecting bwlch with Bryn yr Ŵyn.  

This re-located summit position is not given a spot height on current Ordnance Survey maps and it is approximately 660 metres south south-westward from the previously listed summit position.

The full details for the hill are:

Cardinal Hill:  Pumlumon Fawr

Summit Height:  501.4m (converted to OSGM15, and average of four summit surveys)

Name:  Bryn Llwyd

OS 1:50,000 map:  135, 136

Summit Grid Reference (New Position):  SN 83574 92022 

  

Drop:  30.3m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the summit of Bryn Llwyd, with the summit of Bryn yr Ŵyn on the right and in the background of this photograph

For details on the 1^st Trimble survey and the 2nd Trimble survey that relocated the summit of this hill.

Myrddyn Phillips and Aled Williams (May 2016)

Mapping Mountains – Trimble Surveys – Pumlumon

13.05.16  Bryn yr Ŵyn (SN 839 925), Bryn Llwyd (SN 835 920) and Fedw Ddu (SN 856 917)

Bryn Llwyd (SN 835 920) centre left of photo and Bryn yr Ŵyn (SN 839 925) on right of photo

Having visited Bryn Llwyd (this is a locally known name, used in preference to Esgair Greolen which appears on Ordnance Survey maps) and Bryn yr Ŵyn eight days ago the resulting data for each summit and the drop attained for the higher of the two was of sufficient interest that a second survey was warranted. 

I approached from the south-east from where a minor road heads south from the small community of Penffordd Las (Staylittle).  A passing place proved convenient to park with a few other such places also available near to where a track heads north toward the farm of Nant-yr-hafod.

The forecast for the day was good with sunshine and dry conditions predicted and as I walked up the track the morning’s blue sky pieced the landscape.  Just before the farm the track veers west toward the 488m map heighted summit of Fedw Ddu, and it was here that I met Gareth Griffith who came chugging around the bend with three farm dogs scampering around his vehicle.  I waved a ‘hello’ as I lifted the catch on a gate and he pulled up for a chat.

Gareth Griffith

Gareth had lived at Nant-yr-hafod for forty years and was heading up the hill to feed the sheep.  I explained where I was hoping to go and as some of this land was not a part of open access or did not have a right of way on it, I asked if he minded me using the continuation of the track, he was happy enough for me to do this and we continued our conversation, he told me that he still goes out shepherding on horseback and soon the topic of hill names was mentioned.  He proved extremely knowledgeable and rolled off name after name of the hills and streams above where he farmed.  One name in particular was of interest, it related to the hill that Ordnance Survey maps name as Esgair Greolen, which is the hill I wanted to concentrate the morning’s surveying activities on.  He knew this hill by a different name; Bryn Llwyd, and after mentioning it he said that ‘this name doesn’t appear on the map.’ 

Gareth and his dogs

As Gareth was heading up to the end of the track which is close to the summit of Fedw Ddu I asked if I could have a lift, he kindly said yes and within a couple of minutes I was happily sitting next to him in his vehicle as it chugged its way up the track.  He stopped three times to unload sheep feed and put his dogs in the cage on the trailer at the back.  Rarely do you have an opportunity to make such swift progress up a hill, and as he pulled up at the end of the track I clambered out, put my rucksack on, shook his hand and thanked him in Welsh.

Time to feed the sheep

As Gareth turned his vehicle round I waved my thanks and he disappeared down the hill, leaving me in the early morning sunshine smiling at the thought of how little energy I’d used to get so high.  Within a few minutes I was assessing the land at the bwlch of Fedw Ddu and soon had the Trimble positioned on my rucksack gathering data.

Gathering data at the critical bwlch of Fedw Ddu

Beyond this bwlch a path on the open hillside made good progress toward the summit of Bryn yr Ŵyn.  I planned to take a further two data sets from this first summit, giving five in all when combined with my previous visit, I also wanted to take three data sets from the summit of Bryn Llwyd which would make four in all when combined with those previously taken, and at least seven data sets from the area of the critical bwlch.  All accumulated summit data could be averaged to give the absolute height of each hill, whilst the bwlch data would give an evaluation of the lay of land on the hill to hill traverse, when the data were combined the higher summit would be clarified and its drop obtained.

Once on top of Bryn yr Ŵyn I quickly placed the Trimble on the same point as I had eight days previously and stood a safe distant from it and below it as the first of what proved to be a further 19 data sets were gathered from these hills.  Away to my south south-west Bryn Llwyd looked distinctly lower, as it does from almost every angle that I’ve viewed these hills from.

Gathering data at the summit of Bryn yr Ŵyn

Once a further two data sets were gathered from the summit of Bryn yr Ŵyn I walked over the moor toward Bryn Llwyd and took a further three data sets from its summit.  I placed the Trimble on the ground for two of these data sets and once on top of my rucksack.

Gathering data at the summit of Bryn Llwyd

All that remained was to gather data from the bwlch, this proved fun as a further 13 data sets were taken.  The first of which was from where contour interpolation suggests the critical bwlch to be placed on the ground, I’d taken the third bwlch data set from this position on my last visit and judged this to be visually on the downward slope of the valley to valley traverse, with the traverse from the hill to hill direction just a few metres to the north of this point.

During the remainder of my time at the bwlch I took 12 data sets on what I judged to be on the hill to hill traverse, this heads in a west to east direction.  On every bwlch data set I positioned the Trimble atop my rucksack to give it elevation above the surrounding moor and measured the offset between its internal antenna and the ground with a steel tape.  The furthest point from where I gathered bwlch data from to the west and to the east was at a point that was visually on the upward slope of the hill to hill traverse, with the remainder of the positions approximately 8-10 metres apart, and on the land that I judged to be where the low point of the hill to hill traverse was situated I took data sets five metres apart.  Each point was marked with a flag which proved ideal to visually assess the lay of land.  Once all data sets were complete I packed everything away and started the walk back toward my car.

The march of flags across the bwlch

The positions surveyed at the bwlch are indicated with flags with Bryn Llwyd in the background

Leaving the bwlch I followed a path which crests the connecting bwlch between Bryn Llwyd and Bryn yr Ŵyn and contours around the latter’s southern slopes before joining the inward path and track toward Fedw Ddu.  I’d visited this hill once before and wondered if summit data were possible to collect as its high point is immersed in a conifer plantation.

A forest break conveniently passes over where the spot height appears on the map, and I followed the moss laden ground between the trees until the up seemed to have ended and the beyond seemed to consist of down.  I aimed for a high point at the base of trees and happy that I’d visited what could be construed as the summit I positioned the Trimble to try and collect data, remarkably its 0.1m accuracy level before data should be logged was attained relatively quickly, and as it beeped away collecting its customary 300 data points I stood behind one of many conifer trees, out of sight of the equipment.

Gathering data at the summit of Fedw Ddu

After packing the Trimble away all that remained was to re-trace my inward route, this time on foot, and 6 ½ hours after setting off I arrived back at my car with 19 data points stored in the Trimble. 

  

Survey Result:

The result of the processed data for the first Trimble survey of Bryn Llwyd and Bryn yr Ŵyn was of sufficient interest to warrant another survey, and therefore the following detail takes in the combined results from each survey:

Bryn yr Ŵyn

Summit Height:  499.9m (converted to OSGM15, and average of five surveys and summit relocated to Bryn Llwyd [SN 83574 92022])

Summit Grid Reference:  SN 83919 92571

Drop:  9.9m

Dominance:  1.99%

Bryn Llwyd (significant name change) 

Summit Height:  501.4m (converted to OSGM15, and average of four surveys and Dewey and Uchaf status confirmed and summit relocated from Bryn yr Ŵyn [SN 83919 92571] and new Pellennig hill qualifying on distance) 

Summit Grid Reference:  SN 83574 92022

Bwlch Height:  471.2m (converted to OSGM15)

Bwlch Grid Reference:  SN 83220 91901

Drop:  30.3m 

Dominance:  6.04%

Fedw Ddu

Summit Height:  487.7m (converted to OSGM15)

Summit Grid Reference:  SN 85672 91803

Bwlch Height:  434.8m (converted to OSGM15)

Bwlch Grid Reference:  SN 85176 91727

Drop:  52.9m

Dominance:  10.85%

Post detailing the first Trimble survey of Bryn Llwyd and Bryn yr Ŵyn

For further details please consult the Trimble Survey Spreadsheet