Dikes and pods of pseudotachylite up to one meter thick have been found over an area >50 km² in the same area as shatter cones and other possible features of shock metamorphism in the Beaverhead and Tendoy Mountains in southwestern Montana, defining the allochthonous remains of the Beaverhead impact structure (see also Hargraves et al., Chapter 19, this volume). They are not associated with any tectonic feature in the area and have several features uncommon in pseudotachylites formed by tectonic processes (large size, vesicles, pseudotachylite clasts within pseudotachylite), but which have been documented in pseudotachylites from other impact structures....