A Previously Unreported Locality Record for the Gila Monster (Heloderma suspectum)

Abstract

Although the Gila Monster (Heloderma suspectum) is widely distributed throughout the Sonoran and portions of the Mojave Deserts of the southwestern United States and northwestern Mexico, details of its distribution in California are imperfectly known, due to the apparent rarity of the species in that state. In their review of Gila Monster records for California, Lovich and Beaman (2007) documented only 26 credible sightings during a period of 153 years. In May 2009 another sighting in California was documented by Ruppert (2010a, b) who photographed a specimen in the Providence Mountains, an area known for previous Gila Monster sightings (Lovich and Beaman 2007). In this paper we report the 28 credible record of a Gila Monster in California. In their review of factors affecting the distribution of Gila Monsters in California, Lovich and Beaman (2007) noted that all previous records except one were east of approximately 2116u longitude, corresponding to that portion of the eastern Mojave Desert that receives more than 24 percent of annual precipitation during the warm season (1 July–14 October). They also noted that the majority of records with dates represented observations in April and May. Habitat varied but most observations occurred in mountainous terrain with rocky, incised topography ranging from near sea level to over 1,200 m. Many sightings were in riparian or xeroriparian areas. Based on the ecological attributes considered important in the distribution of the species, Brown and Carmony (1991) and Lovich and Beaman (2007) predicted that future sightings might be reported from the Granite, Whipple, Turtle, and Chemehuevi Mountains of California. To date, that prediction has not been fulfilled to the best of our knowledge. While conducting geological mapping for his Ph.D. dissertation (Haxel 1977), the junior author observed a Gila Monster at close range on the south side of Black Mountain in the southern Chocolate Mountains of southeasternmost California (Fig. 1), at an elevation of 300 6 60 m. This area is underlain mainly by quartzofeldspathic schist (Orocopia Schist), sandstone and argillite (Winterhaven Formation), rhyolite porphyry, conglomerate, basalt, sand and gravel, and colluvium. Much of the landscape is dominated by resistant outcrops and boulders of the basalt that caps Black Mountain. Vegetation, typical of the lower Sonoran Desert, is dominated by sparse creosote bush and cacti, with small ironwood and palo verde trees along drainage ways and washes. The date was 30 April, 1974, during the time of year when most Gila Monsters have been observed in California. The sighting location lies within the rectangle bounded by UTM gridlines E 5 0701000 and 0703000, N 5 3656000 and 3658000 (where E and N denote