In Spring and Summer, Clay-colored Sparrows are similar to Brewer's Sparrows but have a white central crown stripe, dark borders to the cheeks, distinct supercilium, gray hindneck and a dark whisker. Field Sparrow has a pink bill, rusty crown and a white eye ring. In Fall and Winter, Chipping Sparrows are quite similar to Clay-colored Sparrows. Often, they retain some rust in the crown and can be identified by that field mark. Clay-colored Sparrows have pale lores, brown rumps, more distinct whisker and a buffier breast.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.