Declared in 1964, the Park encompasses the highest point of a ridge running east/west along the spine of Tortola. The elevation of the Park ranges from 750 feet at the western end to 1716 feet at Mount Sage, which is the highest point in the Virgin Islands, US and British.

Most of the Park is above 1000 feet, and at this elevation precipitation and cloud cover increase sufficiently to support some forest species (e.g., bullet wood, Manilkara bidentata) normally associated with rain forest in Puerto Rico. Several rare and endangered plant species grow within Sage Mountain. A small area of about 29 and half acres retains much of the character of the original forests that were found at this elevation and in guts in Tortola. This is because the rough boulder terrain here discouraged clearance of vegetation for agriculture apart from some selective logging. Since acquisition by the Trust in 1964, tree planting has been carried out on previously cultivated areas, using West Indies Mahogany and White Cedar, and some natural regeneration has occurred.