Port Isabel & Rio Grande Valley at Port Isabel, Texas, 1934. (USGS Topographic Map)         Source: Geological Survey (U.S.), 1934 Port Isabel quadrangle. 1:31680 series. [Washington, D.C.]: U.S. Geological Survey.                                 [top]         Maps were scanned and text proofread from the original source documents by Murry Hammond. Contact Murry for all corrections, additions, and contributions of new material.