Rattlesnake Mountain, like much of the Metacomet Ridge, is composed of basalt, also called traprock, a volcanic rock. The mountain formed near the end of the Triassic Period with the rifting apart of the North American continent from Africa and Eurasia. Lava welled up from the rift and solidified into sheets of strata hundreds of feet thick. Subsequent faulting and earthquake activity tilted the strata, creating the cliffs and ridgeline of Rattlesnake Mountain. 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. Rattlesnake Mountain is also an important raptor migration path. (See Metacomet Ridge for more information on the geology and ecosystem of Rattlesnake Mountain).