Description: Enlarged dorsals in seven to ten rows, commencing about equal to the insertions of the fore-limbs, and extending posteriorly to the sacrum; median rows of dorsals largest, and progressively diminishing in size as they extend laterally; enlarged dorsals prominently keeled, imbricate, rounded posteriorly; seventeen to twenty-four of the largest dorsals equal to the length of head from tip of snout to posterior border of the interparietal; dorsolateral and lateral folds usually present, nearly always crested with enlarged, spinose scales; usually several lateral clusters of enlarged tubercles; frontal usually entire, sometimes transversely divided; enlarged femorals and tibials larger than any of thedorsals; ventrals mucronate on the gular fold, pectoral,andlateral areas, but rounded elsewhere. Coloration of male topotype: dorsum of body, limbs, head and tail ranging from grayish to darkbrown; limbs and tail ringed with narrow bands of dark brown to black; head finely lined with dark brown; body with nine alternating short bars which extend from the dorsolateral fold to about the median line of the back; dorsal bars about two or three scales wide, and of a dark brown color, edged with pale blue posteriorly; labial regions flecked with gray, as is also the gular region save for a light central area which is a pale tan; pectoral region flecked rather heavily with gray, as are also the undersides of the limbs and tail; abdomen with two elongate sky blue patches which are partially fused medially; preanal region with a blue wash; abdominal and lateral areas necked with numerous individual scales which are a paler blue than the remainder of the body. Measurements of fifty specimens, both sexes: head length, 10.35 mm; head width, 7.75 mm; snout to vent, 42.0 mm; hind leg, 28.0 mm; tail, 66.0 mm

Habitat: This lizard occurs in a wide variety of habitats, such as those with oak, sycamore, desert willow, or chaparral in southern California and thornscrub in Baja California. It habitually perches on rocks or vegetation and retreats underground to escape predators or find shelter. It avoids extreme desert situations.

Range: Its range includes southern California, Baja California, and nearby Pacific islands.

Found in these States: CA

Diet: The diet of Urosaurus nigricaudus was analyzed for the period of March through November 1987 in a xerophytic scrub habitat of the Cape Region in Baja California Sur, México. A great variety of invertebrates were eaten by U. nigricauda, but ants, beetles, butterfly larvae, and wasps were the most important prey types based on number of items consumed, volume, and frequency of occurrence in stomachs. Ants were the most common item, and in autumn leptidopteran larvae became a large part of the diet. The changing importance of prey types with the seasons suggests opportiinistic food habits.

Reproduction: oviparous

Status: Listed as Least Concern in view of its wide distribution, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category.

Taxonomy: