Bendire's and Curve-billed Thrashers have decurved bills, browner upperparts, and less spotted underparts. Juvenile Northern Mockingbird is also mostly gray with spotted underparts but it has white wing patches.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.