Hey Ryan, we have rnage maps for most of the rat snakes of the southwestern U.S. here http://southwesternherp.com/snakes/index.html

Also, there are good range maps in the following books:

Snakes of North America: Eastern and Central Regions. Tennant, Alan and R. D. Bartlett (2000)

A Field Guide to: Amphibians and Reptiles in Arizona. Brennan, Thomas C. and Andrew T. Holycross (2006)

Texas Snakes: Identification, Distribution, and Natural History. Werler, John E. and James R. Dixon (2000) [My favorite...]

Texas Snakes: A Field Guide. Dixon, James R. and John E. Werler (2005)

Lone Star Field Guide: Texas Snakes - Third Edition. Tennant, Alan (2006)

The Complete Suboc: A Comprehensive Guide to the Natural History, Care and Breeding of the Trans-Pecos Ratsnake. Rhoads, Dusty (2008)

A Monograph of the Colubrid Snakes of the Genus Elaphe: Fitzinger. Schulz, Klaus-Dieter (1996)

Amphibians & Reptiles of Texas: With keys, Taxonomic Synopses, Bibliography, and Distribution Maps - Third Edition. Dixon, James R. (2013)
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-Toby Brock
Southwestern Center for Herpetological Research