Montana Valley and Foothills Grasslands

This ecoregion includes grasslands along the eastern edge of the Rocky Mountains (the Rocky Mountain Front) of Montana and Alberta, as well as the semiarid high mountain valleys defined by the Missouri River and its tributaries and the Yellowstone River and its tributaries.  The grassland continues west of  grasslands around Flathead Lake are also included in this ecoregion.

Within the Rocky Mountain Front area are hills and scattered buttes.  Evidence of glaciation is present in many areas, with pothole lakes, glacial moraines, and outwash plains. The grassland surrounding the Little Belt Mountains is limestone-rich,with some caverns in hills east of the Elkhorn Mountains. To the south, the area of the Missouri headwaters and upper Yellowstone tends to be more arid, with sagebrush steppe.  Other areas with sagebrush steppe are the Big Hole valley, Madison Valley, and Beaverhead River valley.

On the Rocky Mountain Front between Choteau, Montana and the Pine Butte Swamp, fossil remains of embryonic, hatchling, juvenile, and adult dinosaurs were found at Egg Mountain in 1979. The Egg Mountain site and the general vicinity has produced remains of adult and embryonic individuals of duck-billed dinosaurs and several other species.  There are several thousand individual fossils.  Each nest held 22 to 30 eggs, hatching babies about a foot long. The eggs appear to represent communal nests (Varrichio et al. 2008). Study of the juvenile dinosaur bones preserved at the Two Medicine Formation indicated that growth plates were present.  Growth plates are discs of cartilage found in birds that are involved in rapid bone elongation during development. The presence of growth plates provided additional evidence that birds are evolutionarily linked to dinosaurs and that dinosaurs were the ancestors of birds (Barreto et al. 1993). Rapid bone growth also implies that these dinosaurs were warm-blooded. Another major implication and finding from the studies of the Two Medicine Formation are that dinosaurs provided parental care, and that that care was provided by both males and females.  This finding indicates that bird parental care originated with their dinosaur ancestors (Varricchio et al. 2008). The climate where the dinosaurs nested is believed to have been semiarid, and this is confirmed by insect trace fossils of wasps and bees and their burrows that are visible in the rocks.  There are so many cocoons that the outcrop is nicknamed Pete’s Pupa Peninsula (Martin and Varricchio 2011).

As a result of the discoveries of dinosaurs on the Rocky Mountain front, the vicinity of Choteau attracted amateur fossil hunters, some of which trespassed on private property and damaged fossil localities (Potera 1995).  In order to get some control over the situation, the Nature Conservancy purchased Egg Mountain, which is now owned by the Museum of the Rockies. The Two Medicine Dinosaur Center in Bynum, Montana, offers field paleontology workshops at sites on the Rocky Mountain front.

The Montana Valley and Foothill grasslands contains a key archaeological site related to the peopling of the Americas.  Evidence from molecular, genetic, and archaeological records suggests that humans dispersed from southern Siberia, in the Trans-Baikal region (subject of a future post) after the last glacial maximum, arriving in the Americas as the continental ice sheet receded and a coastal corridor opened up.  The founding population is believed to be as low at 5,000 (Goebel, Waters, and O’Rourke 2008), and there are believed to have been several waves of migration.

By about 11,000 years before present (BP), a distinctive type of fluted stone projectile point, along with bone and ivory tools, was in use throughout the Americas, known as the Clovis point. Bone and ivory tools were used as foreshafts to attach fluted projectile points, which provided a weapon that could slay mammoths and other large animals, helping to explain how early hunters were able to kill animals 12 feet in height and weighting several tons (Lahren and Bonnichsen 1974).  It is believed that Clovis technology originated and spread throughout North America in as little as 200 years (Waters and Stafford 2007). In 1968 near Wilsall, Montana, in this ecoregion, a child skeleton was found in a burial at the Anzick site. The burial was in a rockshelter near a buffalo jump. The site also included one other skeleton and over 100 stone and bone artifacts (Lahren and Bonnichsen 1974).  One skeleton has been dated to 12,600 years BP. In 2014, the full genome was reconstructed, and the results confirm that the individual was related to the Central and South American Indian community, which is in turn related to the Siberian people (Rasmussen et al. 2014).

The Butte-Anaconda area is the nation’s largest National Historic Landmark District.  However, over 100 years of mining at Butte and Anaconda produced a large concentration of areas in the floodplain that are contaminated with metals.  These areas extend from Butte and Walkerville 26 miles downstream along Silver Bow and the Clark Fork River. Metals also accumulated in the Milltown Reservoir area upstream from Missoula.  These areas are currently in various stages of cleanup as Superfund sites.

A more complete inventory of historic and natural landmarks, parks, and public lands in the Montana Valley and Foothills grassland can be found at sites.google.com/site/enviroramble, to be posted over the next several months.