Nowhere is the volcanic history of the Snake River Plain more obvious. Established in 1924, the 83sq-mi preserve is intriguing and foreboding, a jumble of fissures, lava tubes, spatter and cinder cones, an outdoor museum so intimidating, it has yet to be fully explored. Scientists believe this stark landscape was formed when basaltic lava oozed out of cracks in the earth's crust. So moonlike is the terrain that astronauts were trained here for lunar landings. From a newly remodeled visitor center, 7mi of paved road thread through the volcanic features. In late spring, the black cinder slopes are transformed into a carpet of wildflowers. Daytime temperatures exceed 90ºF in summer; when the park closes in winter, the area is a popular cross-country skiing destination.