Walk - Trethias Farm - Porthcothan

Walk information provided with help from Natural England. Map reproduced by permission of Ordnance Survey on behalf of HMSO. © Crown copyright and database right 2022. Ordnance Survey Licence number 100022021.

Route Description

  1. Coming out of the Trethias Farm campsite,follow the path towards the coast, turning left on the South West Coast Path.
  2. The Coast Path continues straight ahead as it passes the series of headlands, but detouring on the smaller paths hugging the coastline gives an interesting view of the dramatic formations caused by the pounding of the waves.

The bedrock under this area is known as the Trevose Slate Formation. Consisting of slate and siltstone, it was formed in layers at the bottom of a deep ocean, way beyond any land, approximately 364 to 391 million years ago in the Devonian Period. There are deposits of fine material from microscopic sea organisms in the rock. Fossils of planktonic creatures found in the slate along this coastline have helped geologists date these rockbeds.
Breakers rolling in from the Atlantic crash relentlessly around the cliffs, eating into the rock in the places where it is weaker, along fault lines, turning cracks into caves and then washing around the caves to make them bigger. The pressure of the air forced through the cave will cause a blowhole in the roof if it is close to the surface, and as this is also enlarged, so eventually the roof of the cave falls in. The sea continues its erosion, cutting off the outer wall from the coastline, forming first an arch and then an island, which itself gets reduced to a stack, while the cave becomes a cove and finally a bay.
The cliffs are very unstable as a result of all this erosion, so take care around the headlands.
The inlets and coves made this an ideal coastline for smugglers, augmenting their meagre livelihood from fishing with a spot of Free Trade. The rocky caves with their sandy floors made a perfect hiding place for the contraband. Padstow resident William Rawlings wrote to the Earl of Dartmouth in 1765, complaining that his servants had on one occasion encountered no fewer than 60 horses travelling up from one of these beaches 'having each three bags of tea on them of 56 or 58lbs weight'.

  1. Ignore the path inland just before the open access land (unless you want a shortcut inland), carrying on to Porthcothan. There is a network of paths through the heathland here, but the Coast Path continues around the coastline, with more examples of the spectacular coastal erosion.

Please keep dogs on a lead along this part of the walk. There are often sheep grazing here as part of a conservation strategy employed by the National Trust to control the aggressive rank grasses and scrub that would otherwise smother the important maritime grasslands.
Most perennial, slow-growing maritime species occur on sea cliffs. This is not because they need any specific characteristic in this habitat, such as salt, but because further inland they are easily smothered by more vigorous, faster-growing species. The high salt content of the air this close to the sea discourages or kills the terrestrial plants, giving the competitively inferior maritime species a better chance of flourishing.
Unusual plant species occurring along the coast here include the tree mallow, with its massive pink flowers, and the golden samphire. This is an edible plant looking a little like a handful of dwarf beans dotted with tiny yellow flowers. Rock sea lavender also thrives here, resembling heather with its lilac flowers, as does betony, whose purple heads are often humming with insects.
Note the traditional 'curzyway', or 'Jack and Jane', stone walls along the way, where the slates have been stacked in a herringbone pattern before being populated by delicate lichens and stoneworts. Clumps of the pink-headed thrift grow from their tops like thatch, and in places the hedge consists of tamarisk, a feathery-leaved Mediterranean plant which loves dry sandy soil.

  1. At Porthcothan turn left on the road and carry on gently uphill to the road leading off to the left, towards Treyarnon.
  2. Turn left onto this road and follow it past Carnevas on the right and Trethias on the left.

Under your feet at the top of the hill above Carnevas, although you won't see it, the bedrock contains rocks formed from mobile magma, a fluid lava brought to the surface by the eruption of volcanoes at the time that the slate beds were forming. Around Padstow, parts of the coast consist of pillow lava associated with this volcanic activity.

  1. Turn left down the road back to the campsite to leave the walk here, or continue to complete the circuit around Treyarnon. Just after Trethias Farm, turn left onto the footpath cutting across the field and follow it up to the road, turning left here.
  2. Fork left at Treyarnon Farm and walk onto the beach at Treyarnon Bay.
  3. Turn left and cross the beach to pick up the Coast Path again, climbing gently to round the point by Trethias Island and carry on between the farmland and the dramatic cliffs until you come to the path on your left leading back to Trethias Farm campsite.

At low tide a wonderful rock reef appears at the far end of Treyarnon Beach, riddled with rock pools, one of them large enough for swimming and all of them worth exploring. Trethias Island is separated from the mainland by a deep gully, and hides a huge cave which extends under the headland, emerging in the small cove beyond. Please be aware that the tide comes in very rapidly, cutting this area off from the main beach in minutes and flooding the cave.
On the headlands immediately above Trethias Island are three prehistory promontory forts, dating back to the Iron Age. These primitive castles took advantage of the cliffs to protect their communities on the seaward side, building earthwork ramparts on the landward side to give further protection from possible attacks. The remains of these ramparts can be seen under the grass along this part of the Coast Path.
The landowners are working with the RSPB here to protect the corn bunting, which features on the International Union for the Conservation of Nature Red List of Threatened Species as a bird in danger of global extinction. Intensive farming operations in the past destroyed vital habitats and food sources. Traditional methods of land management are being used in many places along the Cornish coastline to restore the corn bunting population. It is a stout, dumpy brown bird which flies off with a fluttering flight and with its legs characteristically 'dangling'. Look out for them in theĀ fields on your left, foraging for food or singing from the fence posts.

Nearby refreshments

In Porthcothan and at Treyarnon YH cafe.

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