The degree to which microhabitat elements such as shade from shrubs are used by lizards and the relative importance of such factors compared to others (e.g., prey availability) remains poorly understood. We examined habitat associations of Desert Horned Lizards (Phrynosoma platyrhinos) to evaluate the determinants of lizard occurrence using surveys along a shrub-steppe bajada in northwestern Utah. We then examined microhabitat preferences of lizards maintained in an experimental arena to explore further the potentially influential factors explaining habitat choice. Greater shrub cover, open understory, and greater cover by cryptobiotic soil crusts were the best predictors of lizard occurrence. While the role of soil crusts is unclear, these other factors may benefit lizards by providing open space for unhindered locomotion and opportunities for temperature regulation through sun/shade shuttling and burrowing. In contrast ants, a primary food source, did not appear to be a significant determinant of P. platyrhinos occurrence. Within the experimental arena, lizards preferred high-shade microhabitats during the day (82% of day selections) and demonstrated strong preference for microhabitats with soil mounds overall (85% of selections). Soil mounds, which form naturally beneath shrubs, tended to warm more quickly in the morning when lizards basked to elevate body temperature, remained cooler in the early evening when high temperatures persisted, and were used as midday and overnight burrow sites. Findings from these studies highlight the important role of abiotic factors associated with vegetation as strong determinants of habitat selection by P. platyrhinos.