Trap rock Trap rock Trap rock, also known as either trapp or trap, is any dark-colored, fine-grained, non-granitic intrusive or extrusive igneous rock. Types of trap rock include basalt, peridotite, diabase, and gabbro. Trapp (trap) is also used to refer to flood (plateau) basalts, e.g. the Deccan Traps and Siberian Traps. The erosion of trap rock created by the stacking of successive lava flows often created a distinct stairstep landscape from which the term "trap" was derived from the Swedish word "trappa", which means "stairway". The slow cooling of magma either as a sill or as a thick lava flow sometimes creates
West Rock Ridge is a dark colored rock, but the iron within it weathers to a rusty brown when exposed to the air, lending the ledges of West Rock Ridge a distinct reddish hue. The rock, which formed 200 million years ago during the late Triassic and early Jurassic periods, frequently breaks into octagonal and pentagonal columns, creating a unique "postpile" appearance. Huge slopes made of fractured rock scree are visible beneath many of the ledges of West Rock Ridge. The ridge is the product of a huge feeder dike that supplied several massive lava flows hundreds of feet deep that welled up