In Craters of the Moon National Monument and the Snake River Plain, volcanic activity has taken a form different from a single great symmetrical cone. Parallel cracks in the earth, collectively called the Great Rift, periodically ooze flows of lava that pile up in horizontal layers. Occasionally, more lively displays create cinder cones, about 25 of them in the park. The panorama of cones here is at the north end of the Great Rift, which extends south more than 50 miles to American Falls.