Trimountain is known for its scenic cliff faces, unique microclimate ecosystems, and rare plant communities.

A prominent landscape feature that rises 500 feet (150 m) above the surrounding valleys, Trimountain is roughly 1.5 miles (2.4 km) long by 1 mile (1.6 km) wide, although the steepness of the terrain makes the actual square mileage much larger.

The mountain formed near the end of the Triassic Period with the rifting apart of the North American continent from Africa and Eurasia.

Subsequent faulting and earthquake activity tilted the strata, creating the cliffs and ridgeline of Trimountain.

Hot, dry upper slopes, cool, moist ravines, and mineral-rich ledges of basalt talus produce a combination of microclimate ecosystems on the mountain that support plant and animal species uncommon in greater Connecticut.