Below lies the dry bed of an intermittent stream called a desert wash. During desert thunderstorms, flash floods rush down mountain slopes and through desert washes to nearby rivers for a short time, but beneath the wash’s sandy surface some moisture remains throughout the year. Non-succulent plants such as palo verde, ragweed, and ironwood thrive along the wash edges because of the underground water supply, and other small plants such as ferns and mosses cling to some shaded embankments. Deer, tortoises, pack rats, rabbits, lizards, and other animals travel along this sand-filled corridor, and rainfall running off a mountain slope can quickly fill desert washes, so flash floods can occur suddenly during desert thunderstorms.