The dikes in Big Bend National Park illustrate the petrologic variety and tectonic setting of Tertiary magmatism in trans-pecos Texas. Most igneous activity occurred between two major episodes in the tectonic history of western North America: (1) late Cretaceous to early eocene laramide compression and (2) late oligocene to recent basin and range extension. Volumetrically minor magmatism occurred during the initial stage of basin and range extension and perhaps during the final stage of laramide deformation. The general geology of the park, including aspects of stratigraphy, structure, petrology, and geomorphology, is best described in the treatise by maxwell and others (1967). The 1:62,500-scale geologic map in maxwell and others' (1967) volume is also available as part of a nontechnical geologic guide to big bend by maxwell (1968). The 1:250,000-scale geologic map by barnes (1979) covers the southern part of the trans-pecos region. A field trip guidebook by maxwell and dietrich (1972) complements these publications. Research results are summarized in guidebooks edited by Dickerson and Hoffer (1980), Dickerson and Muehlberger (1985), and Price and others (1986). In addition, details of the tectonic and magmatic history of the trans-pecos region are provided by Henry and Price (1984, 1985, 1986), Price and Henry (1984), and Price and others (1987).