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Thermal infrared multispectral scanner (TIMS) data were acquired in 1990 over the Piute Mountains, California, to evaluate their usefulness for lithologic mapping in an area of metamorphosed, structurally complex, igneous and sedimentary rocks. The data were calibrated and atmospherically corrected, and emissivity variations in the form of alpha residuals were extracted from which color composite images were made. There was an excellent visual correlation between the units revealed in the color composite image and the lithologic units mapped in the eastern side of the area. It was also possible to correct, improve, and extend the recent map. For example, several areas mapped as granodioritic gneiss had TIMS alpha residual spectra consistent with mafic rocks and were subsequently mapped as amphibolite. The presence of a swarm of mafic dikes, of which only a few had previously been identified, was also revealed. The images also showed color variations in granitoid plutons that correlated with compositional variations previously determined by extensive field and geochemical work, The western Piute Mountains is an area that has proven to be especially difficult to map with field and air photographic methods, due to heterogeneous nature of certain units and various levels of desert varnish. The images permitted the extremely heterogeneous Proterozoic schists, gneisses, and granites to be easily mapped because the small-scale compositional variability was averaged to the TIMS pixel size (12 m x 12 m square). Areal measurements from the images show that the Proterozoic rocks in the Piute Mountains consist of granitoids (approximately 50%), biotite gneiss (approximately 15%), pelitic gneiss (approximately 15%), quartzite (approximately 10%), and amphibolite (approximately 10%). TIMS data can dramatically increase the efficiency and the quality of geologic mapping in well-exposed heterogeneous areas with minimal vegetation cover where detailed mapping of lithologic contacts by traditional methods is unusually difficult.