"watercourse, dry streambed," 1845, a California word, from American Spanish, in Spanish, "rivulet, small stream," from Latin arrugia "shaft or pit in a gold mine," apparently a compound of ad- "to" (see ad-) + ruga "a wrinkle" (see rough (adj.)).
(ə-roi'ō) A small, deep gully or channel of an ephemeral stream. Arroyos usually have relatively flat floors and are flanked by steep sides consisting of unconsolidated sediments. They are usually dry except after heavy rainfall.