The 3 young lava fields found in Craters of the Moon National Monument and Preserve range in age from 15,000 years to 2000 years. Craters of the Moon lava field, the largest of the three fields found along the Great Rift, is made up of about 60 lava flows and 25 volcanic cones that cover 618 square miles. It provides outstanding examples of how molten basaltic rock can solidify into various types of lava. The basic types include block lava (very dense and formed into angular blocks), aa lava (a rough, jagged, clinkery surface), and pahoehoe lava (a smooth, ropy, or billowy surface). Visitors can also see vents, fissures, cinder cones, lava tubes, lava bombs, spatter cones, tree molds, rafted blocks, and many other volcanic features and structures.