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The distribution of the Plateau Fence Lizard (S. tristichus) reaches from Wyoming south through the plains and foothills of Utah and Colorado into New Mexico and Arizona. The Northern Plateau Lizard (elongatus) and the Red-lipped Lizard (erythrocheilus) were once considered separate subspecies; recent taxonomic restructuring reduced them to one species without distinction. In this guide they retain their individuality.
The Northern Plateau Lizard is found in southwestern Wyoming in Sweetwater County with a disjunct population occurring in Carbon County. It prefers the rocky outcrops and large boulders associated with the canyon, sagebrush, juniper woodland, and shrubland communities of the high desert life zone. It is a diurnal insectivore and is active from late April through September. It can be a bit aggressive when handled and is prone to biting.
The Northern Plateau Lizard is commonly found in areas along with the Sagebrush Lizard and it is identified by its more uniform background without dorsal stripes and by lacking the shoulder patch and the black-white-black stripe on the rear of the thigh. In suitable habitat, it is also found in association with the Tree Lizard and it is easily identified by its larger size and by its keeled dorsal scales. The Northern Plateau Lizard seems to enjoy basking more than either of these other two species; it is often found stretched out or perched on large rock surfaces which provide abundant opportunities for thermal heating as well as offering good views of the surroundings.
They are fairly large lizards, usually on the plump side, with snout-vent lengths approaching 3 inches. Their dorsal surface is a rather uniform fleshy-tan to slightly pinkish color with some indistinct mottling or speckling and a few darker slash marks (undulating cross bands) along the dorsolateral margin. The ventral surface is white and both sexes have a pair of bright blue patches on the throat and on each side of the belly—the blue is much more pronounced in males. The scales on the back and legs are overlapping and keeled; those on the belly are smooth and round or polygonal shaped.
Courtship and mating activities usually start in mid May and continue through June. Males defend their territories using posturing displays of head bobbing and push-ups; these also serve as advertisements to attract females in breeding condition. Females lay 5-12 eggs and the larger and more mature females may produce a second clutch. Hatchlings usually begin appearing in July. Sexual maturity is reached in 2-3 years.