Mapping Mountains – Significant Name Changes – Y Trichant – The 300m Hills of Wales

Mynydd Allt y Grug (SN 753 081) 

There has been a Significant Name Change to a hill that is listed in the Y Trichant – The 300m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Mynydd Allt y Grug (SN 753 081)

The criteria for the list that this name change applies to are:

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The hill is adjoined to the Mynydd Du group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with a minor road to its north-west, the A474 road farther to its west, the A4067 road to its south-east and the A4068 road to its north-east, and has the town of Pontadawe towards south-west. 

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

The hill appeared in the original 300m height band of Welsh P30 hills published on Geoff Crowder’s v-g.me website as a twin listed top with the prioritised name given as Tarren y Gigfran, although both this and that of Mynydd Allt-y-grug were given as twin names.

Tarren y Gigfran/ Mynydd Allt-y-grug

338m

SN753081

160

12/165

Two tops of same height - other at SN750079.

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites, and it is the series of Ordnance Survey Six-Inch maps that form the basis of the change in the listed name of this hill.

The Ordnance Survey series of Six-Inch maps formed the base map Ordnance Survey used for many decades leading to the production of the 1:10,000 Series of maps, both have now been superseded by the digitised Master Map.  The series of Six-Inch maps are excellent for name placement and especially so compared to the contemporary Ordnance Survey 1:25,000 Explorer map, and it is the series of Six-Inch maps that prioritise the name of Mynydd Allt y Grug for this hill, with that of Tarren y Gigfran positioned against a small escarpment edge and therefore a feature name, rather than a hill name.

Extract from the Ordnance Survey series of Six-Inch maps

Therefore, the name this hill is now listed by in the Y Trichant – The 300m Hills of Wales is Mynydd Allt y Grug and this was derived from contemporary Ordnance Survey maps and priority status of the name ascertained from the Ordnance Survey series of Six-Inch maps. 

 

The full details for the hill are: 

Group:  Mynydd Du 

Name:  Mynydd Allt y Grug 

Previously Listed Name:  Tarren y Gigfran/Mynydd Allt-y-grug 

OS 1:50,000 map:  160

Summit Height:  338.8m (LIDAR)                                                           

Summit Grid Reference:  SN 75325 08135 (LIDAR) 

Bwlch Height:  148.4m (LIDAR) 

Bwlch Grid Reference:  SN 75768 10169 & SN 75783 10170 (LIDAR) 

Drop:  190.4m (LIDAR) 

 

Myrddyn Phillips (April 2024)