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
Boring Lava Field of Troutdale and more than 32 vents within a radius of Kelly Butte. Mostly small cinder cone vents, these volcanoes also include some larger lava domes from shield volcanoes at Mount Sylvania, Highland Butte, and Larch Mountain. The Boring Lava Field marks the densest volcanic vicinity in this group, with 20 volcanic vents encompassing an area of . It includes more than 80 known small vents and associated lava flows, with more volcanic deposits likely present under sedimentary rock deposits from the Missoula Floods (also known as the Bretz or Ice Age Floods), which took place between 21,000 and 15,000