Ceiswyn Formation

Graig Goch is a 586m high hill in the Gwynedd area in Wales and lying within Snowdonia National Park. The hill falls within the communities of Llanfihangel-y-Pennant and Corris, the summit being located in the former. The hill takes the form of a NE-SW aligned ridge with a broad top which rise to subsidiary tops either side of the main summit. These are the 540m+ top of Mynydd Cedris (OS grid ref SH 707080) and the 504m top of Mynydd Rugog (OS grid ref SH 722092). The hill’s most notable feature is the large cliff which stretches the length of its northwestern face overlooking Tal-y-llyn, in part a major rock-slope failure.

Tal-y-llyn, or Talyllyn, is a small hamlet and former parish in Gwynedd, Wales, situated at the end of Tal-y-llyn Lake close to the village of Abergynolwyn. The parish covered an area of 36,000 acres (15,000 ha). The River Dysynni flows out of the lake at this point, flowing down to enter Cardigan Bay north of Tywyn. Another lake known as Llyn y Tri Greyenyn or Llyn Bach was formerly located close to the border with the parish of Dolgellau. For much of the 19th century, and the first half of the 20th century, the predominant industry in the area was slate mining, in the quarries at Bryn Eglwys and Corris. The Talyllyn Railway was built in the 1860s to serve the quarries at Bryn Eglwys. Although this never reached the lake, and was never planned to do so, the terminus of the railway was in the parish, thereby giving the railway its name. Tourism is now one of the principle industries in the area, and the hamlet includes a hotel and public house. The parish church, St Mary's, dates from the 13th century, with the present structure dating from around 1590. It is a Grade II* listed building. John David Edwards, a cleric and hymn tune composer, is buried in the churchyard.

Tal-y-llyn Lake, (Welsh: Llyn Mwyngil), also known as Talyllyn Lake and Llyn Myngul, is a large glacial ribbon lake in Gwynedd, North Wales. It is formed by a post-glacial massive landslip damming up the lake within the glaciated valley. The hamlet of Talyllyn lies at the west end of the lake.

Tarren y Gesail is a mountain in Snowdonia, north Wales. It is one of the Marilyns of the Cadair Idris group. Lying to the south of Cadair Idris, it and its neighbour Tarrenhendre form the bulk of the Tarren subgroup. The Tarrens rise from the south shore of the Llyn Mwyngil (Tal-y-llyn Lake) and end at the Dyfi estuary. The summit is a grassy ridge, which has a cairn and trig point. The views are extensive to the south and east, with Plynlimon and Cardigan Bay ahead, while the north views are dominated by Cadair Idris and Maesglase to the west. Between Tarren y Gesail and Tarren Hendre lies the Bryn Eglwys quarry, and Nant Gwernol railway station on the Talyllyn Railway, in the ravine of the Nant Gwernol stream. The Tarrerns can be thought of as forgotten mountains of Snowdonia, overshadowed by the popularity of Cadair Idris, occupying the sleepy south-western frontier of the national park.

The Garnedd-Wen Formation (also known as the Garnedd-Wen Beds) is an Ordovician lithostratigraphic formation (a sequence of rock strata) in Mid Wales. The rock of the formation is a mixture of mudstones, siltstones, fine- to coarse-grained sandstones, greywackes and conglomerates. The formation extends from Dinas Mawddwy in the north-east to Tywyn in the south-west.

Craig Cwm Amarch is not synonymous with Craig y Cau but names the headwall of Cwm Amarch on Cadair Idris in the Snowdonia National Park, in Gwynedd, north-west Wales. There seems to be some confusion over naming by people who are not local. 'Craig Cwm Amarch' refers to the crags heading Cwm Amarch, which impinge from the south into the ridge of Mynydd Pencoed, a spur of the Cadair Idris range. The eastern end of Mynydd Pencoed overlooking Llyn Cau is known as Craig y Cau. (Daear Fawr, the ‘large ground’, may refer to an area of the Pencoed ridge. Mountain slopes in Wales are commonly named after the farms to whom the grazing belonged, hence Mynydd Pencoed is named after the farm (its buildings now derelict) at its western foot.

Cyfrwy is a subsidiary summit of Cadair Idris in the Snowdonia National Park, in Gwynedd, northwest Wales. It lies to the west of Cadair Idris and is often climbed with Cadair Idris by taking the Pony Path. The summit is bare and rocky and marked with a cairn. The north and east face has large cliffs. A rock climb/extreme scramble known as the Cyfrwy Arete is found here. This arete is very steep and rope and rock climbing skills will be needed. To the west is Tyrrau Mawr and Craig-y-llyn, while to the south is Craig Cwm Amarch.

Mynydd Moel is the second highest summit of Cadair Idris in the Snowdonia National Park, in Gwynedd, northwest Wales.

Craig-y-llyn is a subsidiary summit of Cadair Idris in the Snowdonia National Park, in Gwynedd, northwest Wales. It lies at the western end of the long Cadair Idris ridge. Its north-facing cwm houses the small glacial lake, Llyn Cyri. The southern flanks have gentle slopes, while the northern are very steep and contain broken crags. The summit is grassy and marked by a few stones. It is often climbed in combination with Tyrrau Mawr.

Gau Graig is a subsidiary summit of Cadair Idris in the Snowdonia National Park, in Gwynedd, northwest Wales. It lies to the east of Mynydd Moel on a broad grassy plateau. It marks the eastern end of the Cadair Idris ridge. The summit is marked by a cairn. To the north are Y Garn and Diffwys, to the west Rhobell Fawr and Aran Fawddwy and to the south are Waun-oer and Cribin Fawr.

Tyrrau Mawr or Craig-las is a subsidiary summit of Cadair Idris in the Snowdonia National Park, in Gwynedd, northwest Wales. It lies to the west of Cyfrwy, and can be climbed by taking a west bearing from the Pony Path at Rhiw Gwredydd. Its north face is a crag, known as Craig-las. Below the crags lies Llyn Cregennen with its small island. The reflection of Craig-las from this lake is one of the famous images associated with Snowdonia. The summit is grassy and marked by a few stones. To the east of the summit lies the large ancient cairn, Carnedd Lwyd. It is often climbed in combination with Craig-y-llyn.

Cadair Idris or Cader Idris is a mountain in the Meirionnydd area of Gwynedd, Wales. It lies at the southern end of the Snowdonia National Park near the town of Dolgellau. The peak, which is one of the most popular in Wales for walkers and hikers, is composed largely of Ordovician igneous rocks, with classic glacial erosion features such as cwms, moraines, striated rocks, and roches moutonnées.