Means "Arroyo of the Alder Trees or Bears."  This is probably the same arroyo that Portol&aacute;'s men named the "Ca&ntilde;ada de los Osos"  (Canyon of the Bears) on September 7, 1769, because of  the excitement they had hunting the numerous bears that were there. <p>An "arroyo" is a waterway  (gully, or wash) which, in the desert, is usually dry, except after a heavy rainstorm.</p>