Mapping Mountains – Trimble Surveys – Y Llethr

03.05.14  Craig Aber Serw (SH 695 265), Craig y Derlwyn (SH 701 259) and Craig y Ganllwyd (SH 707 258)

L-R; Crib y Rhiw (SH 663 248), Y Llethr (SH 661 257) and Rhinog Fach (SH 664 270)

The Rhinogydd are one of the wonders of Wales with their land of rock, heather and bog.  The spine of the mountain range stretches for over 20 miles from Abermaw (Barmouth) in the south to Llyn Trawsfynydd in the north.  Their southern lands give relatively easy walking as rock is interspersed amongst close cropped grass, but their northern lands are the attraction with a sense of lonely wilderness as heather, crag and bog predominate.  Away from the main chain of mountains are lower peaks that match their neighbours in all but altitude and the quantity of footsteps trodden upon them.  Three of these lower hills were my aim for the day; Craig Aber Serw, Craig y Derlwyn and Craig y Ganllwyd.

These three hills are situated directly east of Rhinog Fach and Y Llethr and are joined to these higher hills at a bwlch positioned at SH 686 264.  To their north and east is the forested land of Coed y Brenin, whilst their southern lands descend to the Afon Camlan before rising up to the only 2,000ft mountain in the Rhinogydd that is not part of the main ridge; Y Garn.  I’d often looked down on these hills from the summit of Y Garn, wondering when my first visit would transpire.

As the forecast for the day was dry with high cloud cover I decided that the day had arrived to investigate these hills and do a bit of Trimbling.  Craig y Ganllwyd was of particular interest as it is currently listed as a Sub-Pedwar with 26m of drop based on a 423m summit spot height on Harvey Maps and a 397m bwlch spot height on the Ordnance Survey enlarged Geograph map.  However, this hill is currently listed as a TuMP with 33m of drop based on a 1411ft (430m) height on the Ordnance Survey 1:2,500 map from 1888 – 1889 and the same 397m bwlch spot height.  This latter summit height matches the uppermost contour on current 1:50,000 maps, whilst current 1:25,000 maps only have a c 410m uppermost ring contour.  With two ring contours missing the Trimble should be able to tell which of the two current Ordnance Survey maps is correct and either promotes a Sub-Pedwar to a fully-fledged Pedwar or delete a Tump.

The difficulty with this walk is where to start and finish as the land hereabouts is rather rough and although the proximity of Coed y Brenin gives approach routes via forest tracks it also restricts alternatives.  I decided upon the village of Ganllwyd (SH 726 243) after looking on Google Earth the previous evening for forest tracks, vestiges of paths on the hills and where the conifer plantation existed, as the Ordnance Survey and Harvey map were at odds with one another, the former indicating a greater area of forest on the southern slopes of these hills than the latter.  Google Earth indicates that the Harvey Map is better for forest placement, this map is also easier to use when following forest tracks and paths.  I took both just in case, but used the Harvey for the walk and as I don’t use a hand held GPS, I used a combination of both maps for summit position.  This was the first time I had walked using a Harvey Map in preference to an Ordnance Survey map.

I left Ganllwyd at 8.50am and headed west up a steep paved road beside the Afon Camlan.  Soon I had a choice between a path and the continuation of the paved road which was quickly deteriorating in quality, I decided on the latter although I seemed to remember the path led up to a forest track, which was the one of many that I wanted to be on.  I had used this approach route on many occasions in the past when ascending Y Garn (SH 702 230) but had not been this way in quite a few years.  The paved road soon ended as forest tracks appeared, I contoured left as the track reclaimed its western approach with the river down on my left.  My old approach route to Y Garn used this same forest track and crossed the river, this time I carried straight on and kept the river on my left, this was new ground for me.  Google Earth had indicated that a path continues from the end of the forest track, as indeed does the Harvey and OS map.  As I approached the end of the track I came upon hillsides of felled trees on my right with the rugged rock and heather slopes of my planned last hill of the day; Craig y Ganllwyd, above.  I made a mental note not to descend this way as it looked brutally foolish. 

Approaching the end of the forest track as mature trees give way to felled forestry

The southern flank of Y Garn (SH 702 230) with its summit just visible on right

When the forest track abruptly ended I realised that the fun of the day was just about to begin as there was very little indication of any form of path, the only semblance of a path was on my right which led up to the remains of an old house, I decided that this could not be my route as there didn’t seem to be any path that continued beyond the ruin, I back-tracked down to the forest track and investigated a route continuing in the same direction as the track, within a few metres I gave up as I was in boggy undergrowth of tussock grass and sapling trees with no sign of any form of path at all.  I re-joined the end of the forest track again and went back up to the ruin on my right and this time continued around the ruin and found a semblance of the path descending past the point where I had given up in the undergrowth.  Once down on to the ‘path’ I could see its course on the ground as it headed west in to a land of tussock grass, bog and wilderness.  Remarkably the ‘path’ led past more ruined houses, an indicator when this now lonely valley was once inhabited, either permanently or in summer months with the houses used as shepherds dwellings.

Now a ruin where once there was a small community

Slowly I made progress as the ‘path’ headed toward a solid fence post, painted with a yellow band at the top, I came upon two of these, a thankful sign that I was still on the correct route.  Leaving the busy A470 at Ganllwyd and wandering in to such close but completely different an environment was rather surreal, behind me to my south was Y Garn rising above a desolate wasteland of tussock and bog, in front and emerging above the rising hillsides of more tussock were the higher Rhinogydd.

Just one of a profusion of caterpillars in the undergrowth

The post was an indicator that I was on the 'path'

I wanted to visit the bwlch that connects the three hills I planned to visit with the higher peaks to their west, as I wanted to gather Trimble data to have an accurate drop value for Craig Aber Serw, the map indicated that I would have to contour around the western sides of this hill and walk away from the summit I was aiming for, not a prospect that amuses when the underfoot conditions are problematic.

Bit by bit I gained height and walked from one small grassed and heather bound descending ridge over an intermittent tussock clad bog to another small grassed and heather bound ridge, and so it continued until the bwlch was in sight.  I thought it would take me two hours to get to this point; it took 20 minutes longer than imagined.  I paced up and down the bwlch savouring the moment, as I would, in all likelihood, never return to this particular spot.  Once Five minutes of data was collected I slowly made my way to a vehicle track on the moor that heads from west to east on the northern part of the bwlch, this seems to continue toward a better defined track that descends toward the north.  I only used it for a few hundred metres as it then started descending, whilst I wanted to head up over the moor toward the heather and rock of Craig Aber Serw.

Probably seldom visited by the hill walker; the lonely bwlch at SH 686 264

At the first of three bylchau I wanted to survey with the Trimble

This first hill of the day didn’t disappoint as it is typical northern Rhinogydd countryside; pathless with copious amounts of knee high heather interspersed with rock, crags and an occasional bog.  I placed the Trimble on two high points with the map and my sight indicating that the first was the higher.  At the first point the Trimble was placed on peat is a small clearing of heather, although an erratic rock a few metres away looked about the same height.  The second high point consisted of moss, luxuriant in its greenness amongst the monochrome dullness of lack of highlighted colour.

Gathering data at the summit of Craig Aber Serw (446.3m, SH 69545 26572) with the erratic rock (centre of photo) that could be as high as the heathery summit on right of photograph

Gathering data at the second high point of Craig Aber Serw (442.4m, SH 69639 26355)

The next Trimble placement was at the bwlch between Craig Aber Serw and Craig y Derlwyn.  Not surprisingly this consisted of a tussock bog, once data was gathered I slowly made my way through the pathless assault course and looked down on Llyn y Frân; the lake of the crow, such a tempting and rather mesmerising place, floating in its bed of lonely tranquility with the loud wagh-onk of a pair of Canada Geese the only defining sound to break the unending stillness.

At the second of three bylchau, this one is between Craig Aber Serw and Craig y Derlwyn

I rested for a few minutes, taking photos and just looking, in front was a panorama seldom changed over a multitude of years with Llyn y Frân as foreground to desolation of peak and moor. 

Llyn y Frân as foreground to desolation of peak and moor

Y Garn (SH 702 230) overlooking the forgotten waters of Llyn y Frân

The wagh-onk of a pair of Canada Geese the only defining sound to break the unending stillness

A slow stumble through bog and heather brought me to the high point of Craig y Derlwyn, I took another two data sets one on an embedded large boulder and the second on a rock beside heather that overgrew the uppermost tip of rock by a foot or so.  The time when the Trimble was gathering data enabled me to rest and contemplate the route down to the next bwlch.  After ten minutes of prized data had been collected from each rock I packed the equipment away and headed down through more heather and small crags, taking the only stumble of the day as I fell forward, thankfully with a cushioned impact on heather that had no rock hidden underneath. 

Gathering data at the first high point of Craig y Derlwyn (430.2m, SH 70141 25995)

Looking back at Craig Aber Serw (SH 695 265) from the summit of Craig y Derlwyn (SH 702 259)

Gathering data at the summit of Craig y Derlwyn (430.8m, SH 70245 25934)

The bwlch between Craig y Derlwyn and Craig y Ganllwyd consists of a large flat tussock land of bog that has sapling conifer trees trying to gain ground.  I stumbled my way through this trying to judge where the up and down part of the valley to valley traverse met.  I narrowed the area down to a few metres and picked my spot.  Once picked I tried stamping the tussock ground down to give the Trimble a flatbed to nestle on, as the ground was pushed in by my boots it slowly came back up again, the more I prodded away only the same thing happened, however hard I dug down no solid ground was found, an indicator that the whole bwlch is a bog with a ground swell of water below, thankfully the last few weeks have been relatively dry, otherwise such an exercise may have seen me permanently embedded in the bog.

Approaching Craig y Ganllwyd (SH 707 258) from Craig y Derlwyn (SH 702 259)

At the third of three bylchau, this one is between Craig y Derlwyn and Craig y Ganllwyd

Only one hill remained; Craig y Ganllwyd, I made my way up to its descending stone wall and crossed to the northern side and slowly emerged on to its summit area.  To my eye the hill has three potential high points, one cairned, each had five minutes of data collected on them.  During this time I peered out to the land to my north, wondering if forest tracks would give me an easier but longer route down, although I could see a track amongst the conifers there was no indication of a path to it.  As the third high point achieved its allocated five minutes of Trimble data I decided to attempt a route from the summit direct down to my inward forest track through the large patch of felled forestry that I had earlier dismissed as brutally foolish.

Gathering data at the summit of Craig y Ganllwyd (430.9m, SH 70775 25853)

Gathering data at the second high point of Craig y Ganllwyd (430.4m, SH 70819 25842)

Gathering data at the third high point of Craig y Ganllwyd (430.2m, SH 70824 25866), this proved the lower of the three and is the one marked with a cairn

After clambering over a stone wall and bypassing small crags I ended up in a grassed gulley that led down to the beginnings of the felled forestry, I could now see the forest track which was my way out of all the pathless mayhem.  To my immediate right were young sapling trees and a morass of pathless undergrowth, ahead and to my left were the remains of felled trees that would at least give an easier route.  As I contoured between young sapling trees and felled forestry I looked up and was amazed to see a deer, only the second occasion I’ve ever seen one on the Welsh hills.  Not as grand a sight as many on a Scottish hill, but an unaccustomed rarity on a Welsh one.  It soon majestically bounded out of sight, I headed its way and five minutes later disturbed five deer who quickly lolloped around the hillside out of sight, such elegant animals.

Many hours of pathless heather bashing had taken its toll

My downward route was eased as I came across the remains of a bog strewn bulldozed track that made its way down to the comparative comfort of my inward forest track.  This I retraced, only diverging from it to use the path I had considered on my inward route.  This proved a welcome ending to the walk as the path was old and walled, with moss and beauty to it.  Six hours and fourty minutes after setting out I joined the end part of the steep paved road as it emerged out on to the A470 and the bitter sweet of traffic and civilisation.    

Survey Result:

Craig Aber Serw

Summit Height:  446.3m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 69545 26572 (Trimble GeoXH 6000)

Bwlch Height:  371.2m (LIDAR)

Bwlch Grid Reference:  SH 68640 26449 (LIDAR)

Drop:  75.1m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  16.82% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Craig y Derlwyn

Summit Height:  430.8m (converted to OSGM15) (significant height revision)

Summit Grid Reference:  SH 70245 25934

Bwlch Height:  405.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 69837 26137

Drop:  25.3m

Dominance:  5.87%

Craig y Ganllwyd

Summit Height:  430.9m (converted to OSGM15, Trimble GeoXH 6000) (significant height revision)

Summit Grid Reference:  SH 70775 25853 (Trimble GeoXH 6000)

Bwlch Height:  398.0m (LIDAR)

Bwlch Grid Reference:  SH 70466 25912 (LIDAR)

Drop:  32.9m (Trimble GeoXH 6000 summit and LIDAR bwlch) (Pedwar addition confirmed) 

Dominance:  7.64% (Trimble GeoXH 6000 summit and LIDAR bwlch)

For further details please consult the Trimble Survey Spreadsheet