Mapping Mountains – Summit Relocations – Y Pedwarau - The 400m Hills of Wales

Craig y Greigddu (SH 665 310) 

There has been a summit relocation to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and assisted by Mark Trengove.

Craig y Greigddu (SH 665 310)

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

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills, with this hill being reclassified from the 400m Sub-Pedwar category.  The criteria for this sub category being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Craig y Greigddu and this was derived from research conducted by Aled Williams, and it is adjoined to the Y Llethr group of hills, which are situated in the western part of North Wales (Region C1, Sub-Region C1A), and it is positioned with minor roads to its west north-west and south-east, and has the village of Trawsfynydd towards the north-east.

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

When the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013, this hill was listed with an estimated c 27m of drop, based on the 499m summit spot height positioned at SH 66544 31038 that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and an estimated c 472m bwlch height, based on interpolation of 10m contouring between 470m – 480m that appear on the Ordnance Survey 1:25,000 Explorer map.

Gathering data at the old listed summit

Gathering data at the new listed summit

However, it was not until the survey with the Trimble GeoXH 6000 that an accurate summit height and its position and bwlch height and therefore also drop could be given this hill.  Two surveys were taken for summit position; one at the high point where the 499m spot height is positioned and the second at the high point of a large erratic boulder.  The results appear below:

Old summit position where the 499m spot height appears:  498.896m at SH 66549 31044

New summit position at the top of the large erratic boulder:  499.536m at SH 66565 31003   

The Trimble GeoXH 6000 survey gives the highest ground on this hill as 499.5m positioned at SH 66565 31003, 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 either on Ordnance Survey maps or interactive mapping, 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 considered a relatively recent man-made construct, or the de-twinning of a summit, 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.

Craig y Greigddu (SH 665 310) with the old spot heighted listed summit on the left and the new higher listed summit on the right

Therefore, the height produced by the Trimble GeoXH 6000 survey to the summit of this hill is 499.5m and is positioned at SH 66565 31003.  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 approximately 41 metres south south-eastward from the position of the map spot height and the previously listed summit position, and importantly it is to a different feature.

The full details for the hill are:

Group:  Y Llethr

Name:  Craig y Greigddu

OS 1:50,000 map:  124

Summit Height:  499.5m (converted to OSGM15)

Summit Grid Reference (New Position):  SH 66565 31003

Bwlch Height:  469.2m (converted to OSGM15)

Bwlch Grid Reference:  SH 66658 31203

Drop:  30.3m

 

Myrddyn Phillips and Aled Williams (September 2014)