Malapai Hill is a small volcanic mountain in Joshua Tree National Park near Queen Valley in southeastern California, notable because it rises from a desert landscape more associated with granite than volcanism. Formed about 15.93 million years ago, its basalt intruded into White Tank monzogranite, though whether it was once part of an older volcanic complex or was later exposed by erosion remains uncertain. The hill has twin summits, steep talus slopes, and unusual alkaline olivine basalt containing abundant lherzolite xenoliths, pieces of mantle brought upward by magma. Magnetite near the summit can disrupt compasses, and a 2015 earthquake beneath the hill underscores the region’s continuing geological activity.