Behmn8r,
Short answer: You can't with any certainty.

Long answer: C. b. umbratica (Southern Rubber Boa) was described by Klauber in 1943 based on just two specimens. The other two subspecies were described earlier on the basis of larger samples. Various authors had accepted or rejected the two initial subspecies of C. b. bottae and C. b utahensis but in his 1943 paper, Klauber resurrected both subspecies along with describing the new SRB subspecies.

All three subspecies were described on the basis of a suite of traits but with a certain amount of overlap occurring.

The field guides by Stebbins recognized all three subspecies up until his recent edition was published in 2003 in which he does not recognize any subspecies of the Rubber Boa.
Other authors such as Brown, 1997, still recognize all three subspecies whereas other authors only recognize two (Northern Rubber Boa and Southern Rubber Boa). Still others may now recognize the SRB as a separate species, Charina umbratica.

Since I have been working with the species, it is clear that there is so much overlap in defining traits that there can be no assurance that one can make positive identification as to where a boas originates simply by examination of key characters. For instance, there is about a 40% overlap of defining traits between the Great Basin and Pacific subspecies in Oregon. That is, 40 % of the boas found west of the Cascade Mts. which should be the Pacific subspecies, key out to the Great Basin subspecies. And the reverse is true as well with about 40% of the boas east of the Cascades keying out to be the Pacific subspecies.

Most (but not quite all) boas from about central Tulare County northward to B.C. and eastward to Montana, Wyoming and Utah can be identified as not belonging to the SRB which only occurs in the San Bernardino and San Jacinto Mts. of S. Calif. east of Los Angeles. However there is considerable overlap of traits between the SRB and boa populations that occur elsewhere in Southern Calif. All of those other populations in S. Calif. belong to the Northern clade or Northern Rubber Boa. I have not undertaken the task of determining the percent overlap between the SRB and say the boas found on Mt. Pinos (west of I-5 at the Grapevine just north of L.A.) but I would say it is considerable making positive ID totally unreliable. The only valid method for distinguishing the SRB from other boa populations seems to be via mtDNA analysis.

Richard F. Hoyer

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