Mapping Mountains – Hill Reclassifications – Marilyns

Graig Wen (SH 739 394) – Submarilyn addition

This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Welsh Marilyns.  These reclassification posts will give details of hills where I have had direct association with their change of status, and they will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the TACit Tables booklet

The listing of Welsh Marilyns was published in booklet format by TACit Tables in February 1997 and entitled The Hewitts and Marilyns of Wales.  The Marilyns were originally listed as an all British compilation and were published by Cicerone Press in 1992 in the book entitled The Relative Hills of Britain.  The list compiler for the Marilyns is Alan Dawson.

When the Welsh Marilyns list was published in booklet format there were 156 qualifying hills with a further 27 Welsh Submarilyns also included.  The criteria for Marilyn status being any hill that has a drop of at least 150m, irrespective of their height, with the criteria for Submarilyn being any hill that has 140m or more and below 150m of drop.

The Hewitts and Marilyns of Wales by Alan Dawson

The details for the hill reclassification appear below:

The name of the hill is Graig Wen, and it is situated in the Arenig group of hills in the north-western part of Wales, and is positioned with the B4391 road to its north, the A470 road to its west and the A4212 road to its south, and has the village of Ffestiniog towards the north-west and Trawsfynydd towards the south-west.

Prior to this hill’s addition to Submarilyn status it was listed with an estimated c 139m of drop, based on the 556m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger map and an estimated bwlch height of c 417m.

The Trimble GeoXH 6000 set-up position at the summit of Graig Wen 

As its c 139m listed drop was near the benchmark value of 140m it was prioritised for a GNSS survey and this took place on the 1^st July 2017 and the 23^rd December 2017.  The summit was surveyed on the 1^st July by Myrddyn Phillips and Aled Williams and the col was surveyed on the 23^rd December by Myrddyn Phillips, using a Trimble GeoXH 6000 with collection times of five and six minutes respectively.  These surveys resulted in a 555.6m summit height and a 414.6m bwlch height, with these values giving this hill 141.0m of drop.

The Trimble GeoXH 6000 gathering data at the bwlch of Graig Wen

The addition of this hill to Submarilyn status was accepted by the list author; Alan Dawson, and its new classification augmented in to the listing of Marilyns in December 2017.

The full details for the hill are:

Name:  Graig Wen

OS 1:50,000 map:  124

OS 1:25,000 map:  18

Summit Height:  555.6m (converted to OSGM15)

Summit Grid Reference:  SH 73910 39474

Bwlch Height:  414.6m (converted to OSGM15)

Bwlch Grid Reference:  SH 76316 40341

Drop:  141.0m

Myrddyn Phillips (March 2020)

Mapping Mountains – Trimble Surveys – Arenig Fach

23.12.17  Graig Wen (SH 739 394, only bwlch surveyed)

The bwlch of Graig Wen

I’m not averse to standing in a bog, they do have unusual pleasures that are mainly ones centred on either remoteness or peacefulness, and solitude is also a quality associated with a good bog. 

Bogs are seldom purposely visited by a hill walker, little detail is needed to explain this as they are usually wet, occasionally impenetrable and sometimes oozing with methane, all of these are seldom sought by a hill walker; usually the summit and the view is priority, but a good bog can also give fulfillment.

Today’s bog looked forlorn when I pulled my car up, it looked particularly wet, mist hugged the adjoining hillsides and a slight drizzle was slowly sweeping up the westerly valley. 

I had little option as far as parking was concerned and pulled by car to the side of the B road that makes its way from Llyn Celyn to Ffestiniog and hoped that it would not obstruct any traffic.

Thankfully during my hour’s immersion in said bog few vehicles passed, and all that did so, easily avoided the seemingly abandoned car pulled up on the side of the road, and for any inquisitive driver catching site of me in the bog I suspect I must have looked an unusual site as I spent the majority of the time waiting patiently for data to be gathered as the Trimble sat on top of my rucksack as I stood a number of metres away scribbling all necessary detail in my notebook whilst taking another photograph of the damp and misty land.

The bog in question is the critical bwlch for Graig Wen (SH 739 394) whose summit was surveyed earlier in the year and whose height came to 555.585m (converted to OSGM15).  This bwlch is given a 417m spot height on Ordnance Survey 1:25,000 Explorer maps, if accurate this would give the hill 138.6m of drop.  However, the bwlch contouring on OS Maps (the recent replacement for OS Get-a-map) is between 410m – 415m, if this contouring is correct it would give Graig Wen over 140m of drop which is sufficient for it to be classified as a Submarilyn.  Not news to excite every hill walker, let alone every hill bagger, but new Submarilyn’s do not appear every day of the week.

As I left my car I donned wellies and quickly made my way down beside reed grass and a vehicle track to the point of the bwlch.  Thankfully the bwlch was only a short distance from the B road and although the majority of time I was immersed in its delights proved misty, my car was always in view.

I spent a few minutes assessing the lay of land and followed a water course westward to where the ground visibly descended, and then retraced my steps to where I had initially thought the critical bwlch to lie.  It was here that I took the first of what proved to be four data sets.  The second being where I had walked to, both positions were wet and beside the oozingly green water course.

Gathering the first data set

Gathering the second data set

Wellies were proving essential as I squelched around the bwlch for the next 50 minutes or so, this way and that, balancing from one wet tuft of moorland grass to another.

The third data set was taken from where the 417m spot height is positioned on the ground, visibly this was higher than the position of the first two data sets, but the ground also seemed to ever so slightly rise and then dip again, and it was the water course that led me to thinking where my preferred critical bwlch position to be.

Gathering the third data set

I had a prior appointment with Aled in Porthmadog at 11.00am, so quickly set the Trimble up for the fourth data set on the eastern side of the fence that crosses the area of the bwlch and positioned it beside the continuation of the water course and where the land visually then descended.

Gathering the fourth and last data set

Once the fourth data set was stored and happy with my hour’s activity I abandoned the delights of the bog and walked back up to my car and the onward journey to Porthmadog.      

Survey Result:

Graig Wen

Summit Height:  555.6m (converted to OSGM15, from previous Trimble GeoXH 6000 survey)

Summit Grid Reference:  SH 73910 39474 (from previous Trimble GeoXH 6000 survey)

Bwlch Height:  414.6m (converted to OSGM15)  

Bwlch Grid Reference:  SH 76301 40330

Drop:  141.0m (Submarilyn addition)

Dominance:  25.38%

For further details please consult the Trimble Survey Spreadsheet

For details on the summit survey post of Graig Wen 

Mapping Mountains – Trimble Surveys – Arenig Fach

01.07.17  Pen y Foel Ddu (SH 753 394), Foel Cynfal (SH 749 395), Pt. 548.6m (SH 743 393), Graig Wen (SH 739 394), Moel y Croesau (SH 748 383) and Pt. 369.5m (SH 739 374)

Pt. 548.6m (SH 743 393) with Arenig Fawr in the background

I’ve often looked over to my left when travelling the minor road beyond Llyn Celyn that skirts the wilds of the Y Migneint and heads toward Llan Ffestioniog, and often thought that an approach to the hills taking in Graig Wen looked a boggy and pathless affair, and therefore always shied away from making an ascent from this side, however this was the ascent route suggested by Aled and with a second car left at the entrance to Bryn-celynog it would give an opportunity to visit and Trimble a number of hills, including two marginal Uchaf hills, one of which had been on Aled’s radar for a number of months.

A green track confidently leaves the minor road and looks as if it’s heading straight up toward the hills, unfortunately it abruptly ends with a narrow path continuing next to the course of a fence line, this also soon peters out with only the remnants of sheep paths to follow.

Heading toward the first hill of the day

The fence line led us to ground beside the quietly situated Llyn Cors-y-barcud, which today was a tranquil spot nestled and forgotten amongst its reed grass and bog.  A grassed ridge of sorts headed up and I slowly followed Aled toward the first summit of the day.

Llyn Cors-y-barcud

Aled heading toward Pen y Foel Ddu

Pen y Foel Ddu is the last hill of any subsequent prominence on the eastern side of this compact group, I’d visited this hill in September 2005 when immersed in my basic levelling surveys (BLS) with the resulting drop value being 50ft 6˝ (15.4m).  There is an overgrown cairn at the summit and I quickly set the Trimble up on my rucksack which was positioned on its back as there was a brisk breeze blowing, measured the offset between its internal antenna and the ground below and joined Aled away from the equipment for its five minutes of allotted data collection.

Gathering data at the summit of Pen y Foel Ddu

The next three hills and their respective bylchau and summits came quickly and at each we assessed the lay of land and gathered another five minute data set.  After surveying the summit of Pen y Foel Ddu the next point to gather data from was its bwlch, this consists of a browned water laden bog, and data were gathered from the northern and southern extremities of its watery ground.  Whilst assessing these points a grouse shot up from immediately beside us, a busied flap of wings and off it went, I’ve experienced this on the hill many times over the years, but then three young grouse shot up in all directions, quickly followed by two others and finally a single youngster shot up and away, they flew off in all directions with some of the youngsters following each other and others just skimming the moor grass and coming to rest beyond our eyesight.  This all happened so quickly and straight at our feet, the mother later had the attentions of a hawk which flapped down for the kill, it again shot off heading this time toward Aled and rested in the grass close by using it and also probably us for cover.

Gathering data at one of two points surveyed for the critical bwlch position of Pen y Foel Ddu

Pen y Foel Ddu and its water laden bwlch from the ascent of Foel Cynfal

Heading west the next summit belonged to Foel Cynfal, a relatively flat topped hill without a spot height on any map that I’ve seen.  Once at its summit the ground was assessed and the point judged the highest chosen, and the Trimble set up to gather data.  As I waited beside Aled for the 300 datum points to be stored, the morning’s blue sky had changed slightly with bulbous clouds occasionally blocking the warmth and colour given by the sun, and with a forecast of rain sweeping in from the west at approximately 4.00pm – 5.oopm we knew we could not linger if we were to get back to the awaiting car, dry.

Gathering data at the summit of Foel Cynfal

The next bwlch was positioned to the west and the steep grassed slopes leading down to it helped in assessing its critical point, I headed to its northern extremity and as this looked like the boggied outflow we concentrated our assessment on its southern side, and again the Trimble was set up and gathered its allotted five minutes of data.

Gathering data at the critical bwlch of Foel Cynfal

Our next hill lay on the land heading toward Graig Wen and it was a hill that I’d surveyed with my old wooden staff in September 2005, resulting in its inclusion in the fledgling Uchaf list, I remembered that it has two tops and these were on display as we followed sheep paths and contoured up on ground toward it.  We judged the first top which is the more northerly as the higher.  I set the Trimble up on my rucksack which was laid on its back as the breeze whipped across the hill.  This summit is a fine one and it would be sad to see it go from the Uchaf list if proven to have less that 15m of drop, before heading down to its connecting bwlch we walked to the southern top and peered back and agreed that this was lower.

The land leading toward the two tops of Pt. 548.6m (SH 743 393)

Looking back toward Foel Cynfal

Gathering data at the summit of Pt.548.6m (SH 743 393)

The connecting bwlch proved more expansive than those previously encountered but assessing the lay of land from a number of directions and vantage points helped in judging the placement for the Trimble.  Once five minutes of data were stored the equipment was packed away and we headed up toward the cairned summit of Graig Wen.

Gathering data at the bwlch area of Pt. 548.6m (SH 743 393)

Pt. 548.6m (SH 743 393)

Pt. 548.6m (SH 743 393) with Arenig Fach in the background on the right

I positioned the Trimble on the highest rock of the cairn having moved one or two to accommodate proper placement, then measured the offset to the highest ground at its base and sat with Aled waiting for five minutes of data to be collected.  By now a ribbon of grey cloud was emerging way off on the western horizon heralding the forecast rain, so once the Trimble was packed away I followed Aled back along the broad eastern ridge and down to a land of bog and wilderness.

Gathering data at the summit of Graig Wen

We aimed for a dry hummock close to where pylons crossed this land, this according to LIDAR data that Aled had analysed is where the critical bwlch of our next hill; Moel y Croesau, lay.  I felt knackered when we arrived but the ten figure grid reference obtained from Aled’s analyses soon led me to the correct Trimble placement and again the customary five minutes of data were gathered.

Gathering data at the critical bwlch of Moel y Croesau

The following ascent to the summit of Moel y Croesau seemed to go very quickly, and once there we used the LIDAR placement to zero in on one of two high points.  I soon assembled the Trimble on top of my rucksack which was again positioned on its back.  Our route down was via a gravelled track that heads through these hills that once must have given access to the small mines dotted beside the Afon Llafar. 

Emperor moth caterpillar

Gathering data at the summit of Moel y Croesau

Llyn y Garn with Moel Llyfnant in the background

The gravelled track led down to the remains of the old farm house of Dolddinas and the blue skies of earlier had now been replaced with white cloud as the westerly rain front edged ever nearer.  The track now turned in to a greened path that led up toward Llyn Hiraethlyn, as the high point of this greened path was only just below a Trichant we headed up to claim a new hill for both of us.  Once at the summit the Trimble was quickly set up to gather data, and away to the west the rain front was now depositing its wet stuff on a part of the Moelwynion, so we knew that we hadn’t beaten it and in all likelihood we were going to get wet.

One summit left to visit with Moel y Croesau in the background

The rain massing beyond Trawsfynydd

Gathering data at the summit of Pt. 369.5m (SH 739 374)

The Trimble set-up position at the summit of Pt. 369.5m (SH 739 374)

Following a fence line steeply down beside the remains of a grassed over stone wall led us down to the connecting bwlch.  Thankfully the bwlch was tight and therefore minimum assessment was necessary, as I packed the Trimble away after its data collection the first wind-blown raindrops fell and we quickened the pace on the continuation of the green track that we had left to head up and bag the Trichant.

Gathering data at the critical bwlch of Pt. 369.5m

The path led past the expansive Llyn Hiraethlyn, which must be another forgotten lake seldom visited and yet tranquilly placed.  Contouring the land beyond the path led down toward the old railway line that once went to Y Bala, by now the drizzled raindrops had disappeared east and a slight bright spell developed and remained with us as we headed under the old railway line and down across summer growthed fields with views of Y Garn and past the old farm house of Bryn-celynog to my car.

Llyn Hiraethlyn

Pt. 369.5m (SH 739 374)

Passing under the old railway that once went to Y Bala

A fine view of Y Garn

We’d visited six hills in all and surveyed each summit and five bylchau with only the bwlch for Graig Wen remaining un-Trimbled, with this compact group of hills making a fine circuit and one that portray a wild scene of landscape.  

Postscript:

Since surveying these hills full LIDAR coverage is now available.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height and positional data that is now freely available for England and Wales.  Consequently the numerical details for these hills have been analysed using this technique, and where appropriate these results appear below.

Survey Result:

Pen y Foel Ddu

Summit Height:  531.2m (converted to OSGM15)

Summit Grid Reference:  SH 75395 39452

Bwlch Height:  514.6m (converted to OSGM15)

Bwlch Grid Reference:  SH 75250 39548

Drop:  16.6m

Dominance:  3.13%

Foel Cynfal

Summit Height:  545.5m (converted to OSGM15)  

Summit Grid Reference:  SH 74998 39546

Bwlch Height:  517.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 74884 39528

Drop:  28.1m

Dominance:  5.16%

Pt. 548.6m

Summit Height:  548.6m (converted to OSGM15, Trimble GeoXH 6000) 

 

Summit Grid Reference:  SH 74389 39398 (Trimble GeoXH 6000)

Bwlch Height:  533.0m (LIDAR)

Bwlch Grid Reference:  SH 74326 39304 (LIDAR)

Drop:  15.6m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  2.84% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Graig Wen

Summit Height:  555.6m (converted to OSGM15) 

 

Summit Grid Reference:  SH 73910 39474

Bwlch Height:  414.6m (converted to OSGM15, from subsequent Trimble GeoXH 6000 survey)

Bwlch Grid Reference:  SH 76301 40330 (from subsequent Trimble GeoXH 6000 survey)

Drop:  141.0m (Submarilyn addition)

Dominance:  25.38%

Moel y Croesau

Summit Height:  490.6m (converted to OSGM15)  

Summit Grid Reference:  SH 74812 38345

Bwlch Height:  456.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 75052 38555

Drop:  34.2m

Dominance:  6.97%

Pt. 369.5m

Summit Height:  369.5m (converted to OSGM15) 

 

Summit Grid Reference:  SH 73944 37497

Bwlch Height:  338.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 74077 37523

Drop:  30.7m

Dominance:  8.31%

For further details please consult the Trimble Survey Spreadsheet

For details on the bwlch survey post of Graig Wen