Bighorn Mountains in the context of Bighorn National Forest

Ostracodermi (lit. 'shell-skins') or ostracoderms is an informal group of vertebrate animals that include all armored jawless fish of the Paleozoic Era. The term does not often appear in classifications today because it is paraphyletic (excluding jawed fishes and possibly the cyclostomes if anaspids are closer to them) and thus does not correspond to one evolutionary lineage. However, the term is still used as an informal way of loosely grouping together the armored jawless fishes.

An innovation of ostracoderms was the use of gills not for feeding, but exclusively for respiration. Earlier chordates with gill precursors used them for both respiration and feeding. Ostracoderms had separate pharyngeal gill pouches along the side of the head, which were permanently open with no protective operculum. Unlike invertebrates that use ciliated motion to move food, ostracoderms used their muscular pharynx to create a suction that pulled small and slow-moving prey into their mouths.

The Powder River Country is the Powder River Basin area of the Great Plains in northeastern Wyoming, United States. The area is loosely defined as that between the Bighorn Mountains and the Black Hills, in the upper drainage areas of the Powder, Tongue, and Little Bighorn rivers.

During the late 1860s, the area was the scene of Red Cloud's War, fought between the Lakota peoples and the United States. The Lakota victory in the war resulted in the continuation of their control of the area for the next decade.

The Laramie Mountains are a range of moderately high peaks on the eastern edge of the Rocky Mountains in the U.S states of Wyoming and Colorado. The range is the northernmost extension of the line of the ranges along the eastern side of the Rockies, and in particular of the higher peaks of the Front Range directly to the south. North of the range, the gap between the Laramie range and the Bighorn Mountains provided the route for historical trails, such as the Oregon Trail, the Mormon Trail, and the Pony Express.

The Laramie Mountains begin in northern Colorado and extend discontinuously into southeastern Wyoming between Cheyenne and Laramie and northward to Casper. (By some definitions the Laramies are only in Wyoming.) They are named after the Laramie River, which cuts through the range from southwest to northeast and joins the North Platte River east of the range in eastern Wyoming. The mountains in turn give their name to the Laramide orogeny, the uplift of the North American Plate approximately 70 million years ago that created the present Rocky Mountains.

Powder River is a tributary of the Yellowstone River, approximately 375 miles (604 km) long in northeastern Wyoming and southeastern Montana in the United States. Combined with its tributary, the South Fork Powder River, it is 550 miles long. It drains an area historically known as the Powder River Country on the high plains east of the Bighorn Mountains.

It rises in four forks in north central Wyoming. The North, Red, and Middle forks rise along the eastern slope of the Bighorn Mountains. The South Fork rises on the southern slopes of the Bighorn Mountains west of Casper. The four forks meet on the foothills east of the Bighorns near the town of Kaycee. The combined stream flows northward, east of the Bighorns, and into Montana. It accepts the Little Powder near the town of Broadus, and discharges into the Yellowstone approximately 50 miles (80 km) downriver from Miles City, Montana. The Powder River was so named (in the English language and local indigenous languages) because the sand along a portion of its banks resembles powder or dust.

Natural Trap Cave is a pit cave in the Bighorn Mountains, in northern Wyoming, United States. Excavations in the cave are an important source of paleontological information on the North American Late Pleistocene, due to a rich layer of fossils from animals that became trapped in the cave.