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Pryor Gap, or Pryor's Gap is a pass through the Pryor Mountains. It afforded the shortest and easiest passage between the lower Yellowstone River drainage, flowing eastward through the eastern plains of Montana, and the Shoshone River drainage in the northern half of the Big Horn Basin. The Gap starts about at present day Warren, Montana, and continues along a southwest-northeast axis to near the site of present day Pryor, Montana. Other routes between the eastern plains of Montana, east of present day Billings, and the northern and central interior of the Big Horn Basin were much more difficult to navigate. The Pryor Gap bifurcates the Pryor Mountains into two segments, the West Pryor Mountains and the East Pryor Mountains. Over the years of human occupation, the gap provided the easiest passage from the eastern plains surrounding the lower Yellowstone River drainage to the Shoshone River drainage the Clark's Fork River drainage of the central and northern Big Horn Basin. The Gap was once an ancient river bed of the Shoshone River, which emptied into the Yellowstone River Drainage. In modern times, the Chicago, Burlington and Quincy Railroad extended a railroad grade through the gap from Warren, Montana to Pryor, Montana, and on to Toluca, Ballentine and Billings, Montana.

Formation of the Pryor Gap As An Ancient River Canyon

Pryor Gap was formed as a river canyon for the Shoshone River, passing completely through the Pryor Mountains. In the eons before human occupation, the ancestral Shoshone River issued from the area of the present Absaroka Range and flowed northeast across river valleys and plains to the ancestral Yellowstone River drainage. As the Pryor and the Big Horn Mountains were slowly uplifted about 70 million years ago, the Shoshone River maintained its course and cut a river canyon through the slowly rising Pryor Mountains. At the same time the Bighorn River maintained a separate course to the south, and as the Bighorn Mountains were pushed up the Bighorn River cut a separate and larger canyon completely through the Bighorn range.

At that time, in the area of the central Big Horn Basin there existed a highland area between the Shoshone River to the north and the Big Horn River to the south. This watershed divide kept the two rivers apart and flowing in separate channels into their separate canyons. As time passed, head-ward erosion by a tributary of the Bighorn River finally cut through this highland area and intercepted the Shoshone River so that its flow was diverted, so that the Shoshone became part of the drainage of the Bighorn River. By these erosional changes, the Shoshone River abandoned its course through the Pryor Mountains. The present day Shoshone now flows into the Bighorn River near present day Lovell, just before the Bighorn begins its passage through the Bighorn range, via the Bighorn Canyon.

After the diversion of the Shoshone River, the large dry canyon through the Pryor Mountains remained. Without the scouring water of the flowing river, the center of the canyon slowly filled up with over 900 feet of sediments, washed out of the surrounding East and West Pryor Mountains. However, the partially filled canyon provided a broad an easy path from the eastern Montana river valleys to the Bighorn Basin.

The Pryor Gap as a Corridor from the Eastern Plains of Montana to the Big Horn Basin

After the river bed of the Shoshone was diverted away from the Pryor Gap to the Big Horn River, the Pryor Gap had the potential to become the preferred route, or "pass" between the eastern plains of Montana and the Big Horn Basin. Before the peoples of Asia came to the North American continent, the vast migrating herds of animals on the plains no doubt used the pass for movement between the two areas.

Once migrations of people from Asia had populated the area of present day Montana, the Gap became the preferred route of travel for humans between the rolling plains of Eastern Montana and the Big Horn Basin.

links== Chapter: Pryor Mountains, in book, Billings: the City and the People. Suggests that gap was carved by the Shoshone River, before a barrier between it and the Yellowstone eroded, and the Shoshone then was captured by the Big Horn. This would have been pre-man. Says there are 900 feet of sediments in the center of the gap.

Notes==

An alternative route to the Bad Pass Route. Measure distance from point on big Horn River to junction of Big Horn River, and estimate travel time.

Broader topic== aboriginal routes in Montana.

Prospective illustrations==

A Google earth map with the other routes marked on it, as routes from the plains of eastern Montana to the big Horn Basin, and to the Wind River Country. Why go to the basin or to the Wind River Country.

References

Category:--------- Category:Crow tribe