Abstract The area described here is in McCone County, Montana, approximately 100 mi (160 km) northwest of Glendive and 40 mi (64 km) south of Glasgow, on the east side of the Big Dry Arm of the Fort Peck Reservoir. It is located on the Jordan 1:250,000-scale map, the Fort Peek Lake East 1:100,000-scale map, and the Bug Creek 1:24,000-scale topographic map. The Bug Creek area (Fig. 1) is reached by proceeding south on Montana 24 for 24 mi (39 km) from the Fort Peck Dam or north 25 mi (40 km) from the intersection of Montana 200 with Montana 24. At this point a dirt road heads due west for 2.5 mi (4 km), then swings north at the rim of a mesa, and then swings south to the crossing of Bug Creek. The dirt road is passable by any vehicle when dry; four-wheel drive is required when the road is wet. The dirt access road is about 2.5 mi (4 km) south of the crossing of Montana 24 over the South Fork of Rock Creek and 5.5 mi (8 km) south of the road sign to Rock Creek State Park. More than 2 mi (3 km) west of Montana 24, the land is part of the Charles M. Russell National Wildlife Range. Much of the other land is controlled by the U.S. Bureau of Land Management (BLM); some is privately owned. Collection of vertebrate fossils on federal land is by permit only. No permission is required to examine exposures on federal or state land;

Over a century has passed since 1901 when W.T. Hornaday showed a fragment of a horn of Triceratops found in the valley of Hell Creek to H.F. Osborn at the American Museum of Natural History. The following year Osborn's assistant, Barnum Brown, was dispatched to eastern Montana and began investigations of its geology and paleontology. By 1929, Brown had published a geological analysis of the rocks exposed in the southern tributaries of the Missouri River, named the Hell Creek Formation, and published studies of some of the dinosaurs discovered there. Parts of his collections of fossil mollusks, plants, and vertebrates contributed to research by others, particularly members of the U.S. Geological Survey. From 1930 to 1959, fieldwork was slowed by the Great Depression and World War II, but both the continuing search for coal, oil, and gas as well as collections of fossils made during construction of Fort Peck Dam set the stage for later research. Field parties from several museums collected dinosaurian skeletons in the area between 1960 and 1971. In 1962, concentrations of microvertebrates were rediscovered in McCone County by field parties from the University of Minnesota. Ten years later, field parties from the University of California Museum of Paleontology began collecting microvertebrates from exposures in the valley of Hell Creek and its tributaries. The research based on this field research provided detailed geological and paleontological analyses of the Hell Creek Formation and its biota. In turn, these contributed to studies of evolutionary patterns and the processes that produced the changes in the terrestrial biota across the Cretaceous-Paleogene boundary.