Mapping Mountains – Summit Relocations – 200m Twmpau and Y Trechol – The Dominant Hills of Wales

Crugiau Maen Saeson (SN 141 456) 

There has been a Summit Relocation to a hill that is listed in the 200m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from detail on contemporary maps produced from Ordnance Survey data and LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Crugiau Maen Saeson (SN 141 456)

The criteria for the two listings that this summit relocation applies to are:

200m Twmpau - Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 200m Twmpau by Myrddyn Phillips

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddn Phillips

The name the hill is now listed by is Crugiau Maen Saeson and this was derived from local enquiry, and it is adjoined to the Mynydd Preseli group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned encircled by minor roads, with the B4546 road farther to its north-east and the A487 road farther to its south-east, and has the town of Aberteifi (Cardigan) towards the east.

When the original Welsh 200m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a summit height of 205m, which is adjoined to a triangulation pillar with a flush bracket height of 205.224m positioned at SN 14170 45534 and which appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

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

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Crugiau Maen Saeson (SN 141 456)

The summit height produced by LIDAR analysis is 205.3m positioned at SN 14104 45618 and SN 14106 45618 which corresponds with the position of an ancient tumulus, and this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is judged to be a relatively recent man-made construct, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

Therefore, the summit height produced by LIDAR analysis is 205.3m and this is positioned at SN 14104 45618 and SN 14106 45618, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and is positioned to a different feature approximately 90 metres north-westward from where the originally listed summit is positioned. 

 

The full details for the hill are: 

Group:  Mynydd Preseli 

Name:  Crugiau Maen Saeson 

OS 1:50,000 map:  145

Summit Height:  205.3m (LIDAR) 

Summit Grid Reference (New Position):  SN 14104 45618 & SN 14106 45618 (LIDAR) 

Bwlch Height:  c 127m (interpolation) 

Bwlch Grid Reference:  SN 15174 41089 (interpolation) 

Drop:  c 78m (LIDAR summit and interpolated bwlch) 

Dominance:  38.13% (LIDAR summit and interpolated bwlch) 

 

Myrddyn Phillips (March 2023)