The San Pedro River is the last major free-flowing river in SE Arizona. It captures drainage from nearly a dozen mountain ranges to its confluence with the Gila River near Winkelman, Arizona. The annotated image on this postcard illustrates the complexity of sediment stratigraphy of the river channel. Ornithologists come from all over to view the migratory birds that inhabit the San Pedro River and surrounding riparian areas. Photo and annotation by J.P. Cook (AZGS).