The nesting habits of Rock Wrens (Salpinctes obsoletus) were investigated at high altitude in the Sierra Nevada Mountains of California. Nests were built in cavities located under rocks or within rocky outcrops. The birds placed small, flat rocks inside the cavity to form a foundation for the nest cup, at the mouth of the cavity effectively decreasing the size of the entrance, and outside the nest cavity as if in a pathway. Eggs implanted with thermocouples provided records of egg temperature from which the females' incubation patterns were determined. Females roosted in the nest cavity and began diurnal incubation 3 days after beginning the clutch. Constancy of incubation was 71.0%, and mean egg temperature during full-time incubation was 34.4 C. Diurnal attentive bouts lasted a mean of 45.2 min and inattentive bouts 17.4 min.