Marsabit is a massive basaltic shield volcano located 170 km E off the center of the East African Rift. There are 22 maars and 180 cinder cones on its slopes, most of which are concentrated along NW- and NE-trending belts that cut across the thickly vegetated summit region. The main phase of shield construction occurred during the Pliocene. Quaternary activity shifted to explosive activity that formed maars accompanied by further extensive effusion of lava flows. The youngest dated lava flow has a Potassium-Argon age of 68,000 +/- 16,000 years, but more recent activity has also occurred. The youngest lava flows are unvegetated, and Key (1987) mapped the post-shield cinder cones as Pleistocene-to-Recent in age.