Mapping Mountains – Trimble Surveys – Y Llethr

21.09.14  Craig Wion (SH 664 319), Pt. 499.5m (SH 665 310), Pt. 508.8m (SH 663 308), Pt. 518.5m (SH 663 306) and Pt. 497.2m (SH 661 303)

The central ridge of the northern Rhinogydd - a land of rock and heather

In the western part of north Wales is a land made of hard sedimentary rock where mountain peak and wild heather moor is interspersed with desolate bog and openness seldom found in northern Wales.  When walking in to this country there is a feeling of visiting a land that time has forgot.  The land in question is the Rhinogydd, a unique landscape in Wales where a continuous ridge stretches from its grassier southern lands in to its central and northern realms where great gaping gaps are met with up thrusts of rock.  It really is quite a magical place.

This was another walk suggested by Mark, who along with his ex-working colleague and good hill walking friend; Dave Middleton, planned on visiting the central section of the northern Rhinogydd from Craig Wion to Bwlch Tyddiad.  Mark asked if I would like to join them, as I’d only walked this part of the ridge in its entirety once before I jumped at the chance.  My memory from my previous visit was one of rock canyons and numerous hills all joined by a narrow path that if lost foretold a struggle amongst wild land of heather, bog and crag.

We met at Y Bala and proceeded in one car to the beauty of Cwm Bychan which was resplendent in early autumnal sunshine.  We parked at the head of the cwm next to the Cwm-bychan farm house where there is a grassed parking area with an honesty box for the parking fee of £2.00 per car and £1.00 per person.

As we headed back down the lane to join the path that headed up toward the bwlch between Clip and Craig Wion, we stopped and framed the impressively looking Carreg y Saeth against the lapping waters of Llyn Cwm Bychan.  Carreg y Saeth justifiably appears on the front cover of the 1^st edition of Y Pedwarau.  It looks a stunning hill guarded by typical northern Rhinogydd rock and heather.

Carreg y Saeth framed by Llyn Cwm Bychan

Once our path was found it led up through hill sides of heather, now with their purples dying back to dull browns, their ebbing colour still contrasting subtly with the yellow and green of the gorse. 

The subtle colour maze of heather and gorse

As height was gained Clip rose up ahead, another impressive hill with sides of rock giving way to lower ground of tussock and bog, what marvellous country.  At this stage Mark and Dave were about ten minutes behind me as I steadily made progress up to the first bwlch of the day.  The afternoon cloud had yet to bubble up and with blue skies the sun’s warmth illuminated the land.

So good, it had to be included twice - Carreg y Saeth

Clip (SH 654 329) rising out of its lower heather clad land

The first of many point’s to survey was the critical bwlch of Craig Wion, there proved two possibilities for its position with a hummocky lump bulging up between, the north-westerly option looked the lower and this is where the Trimble was placed for its five minutes of data collection.  As the equipment was being closed off Mark and Dave appeared, perfect timing.

Gathering data at the critical bwlch of Craig Wion

We initially found vestiges of a path heading toward our first summit of the day; Craig Wion, this was soon lost but reappeared higher up.  Behind us Clip rose almost as a black face of rock with Craig Ddrwg continuing ever northward.  This section of ridge from Clip to the Pedwar of Craig y Gwynt is another magical place to investigate.

Dave and Mark admiring the rock face of Clip and Craig Ddrwg

Ahead lay the small cairned summit of Craig Wion with its slightly rounded shape bulging with rock.  As the Trimble gathered its customary five minutes of data we took a break and relaxed with food in welcome sunshine.  To our south lay a jumble of rock strewn hills, one lump after another, all seemingly merging in to one another.  I’d come prepared with a number of ten figure grid references which Mark fed in to his GPS in a steady stream of data through the day.  Each helped pinpoint where the map spot height or interpolation suggested the survey point to be on the ground.

The rounded rock strewn summit of Craig Wion

Gathering data at the summit of Craig Wion

As we left the summit of Craig Wion we headed toward the first of four potential critical bwlch positions for a 499m map height hill that is listed with c 27m of drop.  In affect this hill could change from its current Sub-Pedwar status to a fully-fledged Pedwar, or jump up in altitude rank to a Dewey or for those interested in Sub-Deweys it could find its way in to this sub-set of hills.  To be sure that the correct lowest bwlch was surveyed each in turn would need Trimbling.

The narrow path continued down toward the first of the four bylchau with land ahead now rising as each rocky top became more distinguishable, as we descended I noticed a substantial hill down on our right, we checked the map and couldn’t find where it was situated.  As we neared the bwlch it quickly disappeared out of sight, I promised myself it was something to investigate in the future.

Each of the four bylchau were visited, with each bwlch bisected by lumps of heather and rock emerging up out of the ridge, the narrow path continued like a roller coaster as it wound its way over the land.  When at each bwlch it was similar to being in a narrow tussock grassed encampment beside rising sides of rock.  The land we were walking on was proving impressive in nature and if not for the ten figure grid references directing us toward each Trimble placement we may have become marooned in a complicated land where map contouring could easily go wrong.  Considering how narrowly defined some of these bychau were the Trimble was achieving its 0.1m accuracy before data can be logged remarkably quickly.  Only once did it struggle and this was when a vertical bank of cliff rose directly above it.

Once the four bylchau had been surveyed we headed up to the summit of the 499m map heighted Sub-Pedwar.  The ten figure spot height grid reference placement took us to the northern edge of its summit plateaux where small squared rocks all neatly stacked together but split from weathering where trying their utmost to topple over a cliff, the Trimble was placed on their high point and I willed it to stay in position.

Typical northern Rhinogydd land

Balanced on the edge of a cliff, the first option for the summit of Pt. 499.5m came to 498.896m (converted to OSGM15) at SH 66549 31044

About 100 metres to the south lay a large erratic boulder which looked slightly higher than where the 499m spot height is positioned on the ground, and whilst Mark and Dave went over to investigate it I took a reading with a small spirit level and Dave then did likewise sighting back toward me.  We all agreed that the erratic boulder looked higher.  But would it prove to be over 500m in height?  Data were collected from its top as we gazed back on the wild land we’d walked through and looked toward the maze of rock ahead.

Dave standing on the top of what proved to be a new Pedwar

Gathering data at the second option for the summit of Pt. 499.5m, this came to 499.536m (converted to OSGM15) at SH 66565 31003

The descent from this summit takes you down a steep cleft in the rock to a lower boulder field before the customary narrow tussocked bwlch is crossed to a steep ascent on a peat path.  It would be a shame to lose this hill from the list of Sub-Pedwarau to the higher echelons of 500m hills as it is a fine hill by any standard.

As we crested the opposing ground at the top of the steep peat path I veered rightward to visit a small hill just to our west.  Mark left Dave and I to our bagging need and said he was going to sit and grumpily eat his trail mix as he was going to have nothing to do with these smaller prominence hills.  Whilst at its summit I headed toward yet more cliffs to photograph the current Sub-Pedwar in late afternoon sunlight and stepped straight in to a hole on my way back toward Dave, who was sitting on a rock taking in the view.  The small hole proved to have sides of rock which scraped my lower leg meaning that I was sporting a bloodied wound when we re-joined Mark.

The summit of the new Pedwar is the large erratic boulder on the right of photo.  The 499m map spot height is positioned at the summit on the left of photo.

However, before re-joining Mark we followed his tracks up a slender path on the edge of a small drop as it traversed a crag, what marvellous land.  This delightful little occupier of mind and soul popped us out near to the top of the hill that is listed in Michael Dewey’s list as Moel Morwynion, which in his notes within his 500-Metre list has ‘Authors name from llyn 600 metres to south west’.  It would be good to one day find a locally known name for this hill.  As the Trimble gathered data from the high point Mark kindly did running repairs to my leg and covered a formidably sized plaster with some ointment, I then slapped it on my leg and watched as blood oozed out from the sides, mmmmm yummy, time for a sandwich.

Gathering data at the summit of Pt. 518.5m

Dave admiring the view

By now eleven surveys had been conducted and there was only one hill left to visit, this is listed under the point notation in Y Pedwarau as no suitable historical or local name is known for it by the authors.  I’d previously surveyed this hill with my old staff and obtained a drop of 102 ½ft / 31.2m, noting that ‘difficult measure on rock and heather, two summits, southern one has large cairn’.  As ever with these old staff surveys I take great delight in comparing their drop result to more accurate surveying which today was being done with the Trimble.

Once at its bwlch the Trimble was positioned on its improvised Tripod and again it reached its 0.1m accuracy relatively quickly.  Once data were collected we headed up to the 497m map heighted summit.  By the time I had arrived Mark and Dave had pin-pointed the highest point, soon the Trimble was in position and I grabbed a bite to eat and watched as the sun sank behind a narrow bank of evening cloud as the sea turned golden in its glow.

The penultimate survey of the day at the summit of the Sub-Pedwar

Sea turning golden in the sun's glow

This Pedwar also has an adjacent 496m map height top which has a large cairn beside it; we just had time for me to gather another five minute data set from this point before it was time to head down.  As the Trimble gathered data I stood and looked out to sea as the sun cast evening colour from behind its narrow cloud bank, to be on a hill as daylight turns to night is a magical experience. 

Last survey of the day as the light dims from the evening sky

Casting colour from behind cloud

As we left the last summit of the day the sun was playing light upon the land with mauve tinged highlighted cloud nestling above a sea of orange.  As the sun emerged from its cloud hiding it turned the land a succulent rich hued red with black of foreground hills being off laid with the bluish grey of the slither of Pen Llŷn.

Rich colours highlighted against the black outline of the Rninogydd

The walk down the Roman Steps proved enjoyable as light dwindled from the land, and as we entered the lower reaches of our route back to Cwm Bychan, darkness fell upon us with just a serene afterglow highlighted on the lake.  It proved a fitting end to a walk in a rather special area of Welsh upland.

 

Darkness descends on Llyn Cwm Bychan.  Photo: Mark Trengove

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 LIDAR has been used in preference to that produced by the Trimble. 

Survey Result:

Craig Wion

Summit Height:  565.6m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 66424 31950 (Trimble GeoXH 6000)

Bwlch Height:  484.6m (LIDAR)

Bwlch Girf Reference:  SH 65773 32880 (LIDAR)

Drop:  81.1m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  14.33% (Trimble GeoXH 6000 summit and LIDAR bwlch)





Pt. 499.5m

Summit Height:  499.5m (converted to OSGM15) 

Summit Grid Reference:  SH 66565 31003 (summit relocation)

Bwlch Height:  469.2m (converted to OSGM15)

Bwlch Girf Reference:  SH 66658 31203

Drop:  30.3m (400m Sub-Pedwar reclassified to Pedwar)

Dominance:  6.08%

Pt. 508.8m

Summit Height:  508.8m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 66387 30869 (Trimble GeoXH 6000)

Bwlch Height:  492.0m (LIDAR)

Bwlch Grid Reference:  SH 66473 30805 (LIDAR)

Drop:  16.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  3.29% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Pt. 518.5m

Summit Height:  518.5m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 66363 30620 (Trimble GeoXH 6000)

Bwlch Height:  461.4m (LIDAR)

Bwlch Grid Reference:  SH 66597 30833 (LIDAR)

Drop:  57.1m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  11.01% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Pt. 497.2m

Summit Height:  497.2m (converted to OSGM15)

Summit Grid Reference:  SH 66182 30317

Bwlch Height:  465.3m (converted to OSGM15)

Bwlch Girf Reference:  SH 66219 30458

Drop:  31.8m 

Dominance:  6.41%

For further details please consult the Trimble Survey Spreadsheet