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The core range of the arroyo willow includes the California Coast Ranges and most of central northern California. It extends north into Oregon, and south just into Baja California. S. lasiolepis var. lasiolepis is found in disjunct occurrences of moderate size in Idaho, the Mogollon Rim-White Mountains across Arizona's transition zone, the coastal ranges of Oregon, central Washington, two northern mountain regions of New Mexico, and two mountain regions of Coahuila.
S. lasiolepis is a deciduous large shrub or small tree growing to 10 m (33 ft) tall. The shoots are yellowish brown and densely hairy when young. The leaves are 3.5–12.5 cm long and broadly lanceolate in shape. They are green above and glaucous green below. The undersides are covered with whitish or rusty hairs which gradually wear off during the summer. The flowers are arranged in yellow catkins 1.5–7 cm long which are produced in early spring.