It is a large, slender colubrid snake with a long head, large eyes, and smooth dorsal scales. Each dorsal scale contains two apical pits. The dorsum is uniform olive or reddish brown without dark markings on a cream-colored background. Yellowish or greenish coloration extends from the lower sides of the body to the venter. The iris is yellow-green.
Taxonomic remarks
Dowling and Price have placed this snake in its own genus based on immunological data, but complications with the data set and the mode of analysis indicate that it is best to regard this species as a member of the rat snake genus, Elaphe, until further data become available. No attempts have been made to characterize genetic variation across the geographic range of E. rosaliae. An understanding of that variation is needed to determine whether genetically differentiated populations exist within E. rosaliae. The difficulty in obtaining the requisite material for such a study makes it likely that novel techniques, such as extracting DNA from preserved specimens, will be needed to address this problem.
Distribution
The Baja California rat snake ranges from extreme southern Imperial County southward into Baja California to Cabo San Lucas. Over at least the northern half of its range, it is known from widely disjunctive locations. Its known elevations range from near sea level to ca. 300 m. In the United States, E. rosaliae is known from only one road-killed specimen CSDSNH 644161 taken 26 May 1984 on Interstate Highway 8, east of Mountain Spring, California. Although Stebbins and others believe this locality to be genuine, some have questioned the validity of this record.
Life history
The life history of E. rosaliae is virtually unknown. The species seems to be nocturnal or crepuscular and may be surface active during daylight hours under suitable conditions. Nothing is known about reproduction or growth except that clutches with an unspecified number of eggs have been laid in captivity. The few data on diet and behavior are based on captive specimens and are difficult to interpret in the absence of data on this snake under field conditions. If similar to other rat snakes, it climbs easily and adults are probably long-lived. No data on movement, colonization abilities, or the potential predators of this taxon exist.
Habitat
Elaphe rosaliae is largely confined to mesic and dry desert habitats in the immediate vicinity of small springs but individuals have also been observed on hillsides and dry mesas away from water sources. The habitat components critical to this snake have not been identified precisely, but it may require some kind of shrub or tree with a moderately dense crown in which to take refuge because it has been taken in native fan palms, date palms, mesquite, palo blanco, palo verde, and creosote bush associations in the past. The locations of oviposition sites are unknown.
Status and habitat recommendations
The California State Government classes its status as "Special Concern". It notes that the snake is an infrequently observed species avidly sought after by amateur, scientific, and professional collectors alike. Because of the uncertain status of the single record from California, it believes that it should remain protected until further information regarding its distribution within the state becomes available. The California Department of Fish and Game Habitat Conservation Planning Branch recommends that intensive surveys of habitats with shrubs or trees having a moderately significant crown in Imperial and San Diego counties are needed to determine whether this snake is really part of the herpetofauna of California. If populations are discovered, the Planning Branch states that the local habitat needs to be protected from modification and potential collecting, and some kind of monitoring for this taxon should be initiated.
