This site is of disputed antiquity. If you have any information that could help clarify this site's authenticity, please post below or leave a post in the forum.
The map of Penwithian round barrows in Cheryl Straffon's revised "The Earth Mysteries Guide to Ancient Sites in West Penwith" (2010) shows a coastal barrow at Roskestal.
There's nothing listed on Pastscape or the Cornwall and Scilly HER, although there have been various finds of stone tools on the cliffs here, as well as a prehistoric field system.