What is a mesa?

A mesa forms where a hard, erosion-resistant layer of rock caps softer layers below, protecting the top while the land around it wears away. Over millions of years this leaves a tableland standing high above the plain with cliffs on its sides. The word 'mesa' is Spanish for 'table', a name given by Spanish explorers in the American Southwest. As a mesa erodes further, it can shrink into a smaller butte and eventually a slender pinnacle or spire. Monument Valley on the Arizona–Utah border is famous for its mesas and buttes.