The main vegetation types on the hill are western lowland heath and scrub. The heath consists of a mixture of heather, bell heather and western gorse replacing E. cinerea in wet areas. Bilberry and tormentil also occur. On the deeper soils European gorse, bracken and bramble are the dominant scrub species. The bare slopes of the old china clay works are where western rustwort occurs. By 2004 the liverwort was known from fourteen sites within three SSSIs, making Cornwall the main stronghold globally. The nationally scarce moss known from only two sites in Cornwall also occurs on Tregonning Hill. As of 7 September 2010 the condition of the SSSI was considered to be ″unfavourable declining".
Tregonning Hill is a detached outcrop of the Cornubian batholith. The granite has been altered by kaolinization resulting in china clay. Disused pits, gullies, waste-tips and debris litter the hillside. While visiting the area in 1745, William Cookworthy, a Plymouth chemists observed a very fine clay being used to repair furnaces. Cook had previously discovered how to make hard porcelain, which at that time was imported from China. He subsequently searched for a suitable clay so that porcelain could be made in Europe and found that when mixed with china stone the clay from Tregonning Hill was suitable. He took leases on the hill and exported the clay from Porthleven to Plymouth. In the 1870s china clay from Tregonning, and a 30 to 40 acre quarry at Tresowes on the western side of hill, was shipped from Porthleven; the amounts were 92 tons in 1876, 130 in 1877, 61 in 1878, 136 in 1879 and none in 1880. Export of china clay and fire bricks to New York via Hayle first started in August 1880. In 1882, Tresowes produced 700 tons, while Tregonning Hill produced 500 tons. In the early 1870s the Tregonning Hill China Clay and Brick Works was established by William Argall. He had the financial backing of two ironfounders; William Harvey of Hayle and John Toy of Helston. A Scrivener kiln is the only part of the brickwork's which can still be seen. In the early 1880s, ten people were employed at the brickworks and the approximate annual number of bricks produced was 150,000. According to Historic England the partly ruinous kiln is probably of the 18th-century and in 1987 was given a grade II listing. An Ordnance Survey map published in 1907 indicates the site was disused by then. An elvan quarry was in operation on the summit in 1879.
Religion
In 1880 The Cornishman reported on the annual custom, by the Ashtown Free Church Sunday scholars, to walk in procession to the ″old amphitheatre″ for a sermon.
