To British America, and from the Missouri and White Earth rivers to the " summit " of the Rockies; but in 1861 and 1863 it was reduced, by the creation of other Territories, to its present boundaries.
The main areas are on the two flanks of the Rockies, with two smaller fields in the Parks.
End of the Southern Rockies extends across the Colorado line into southern Wyoming.
An outlying member of the Rockies which boldly interrupts the continuity of the plains in north-central Wyoming.
In the region between the Northern and Southern Rockies, the plains are interrupted by minor Mountain groups, volcanic buttes and lava flows, among which the Leucite Hills and Pilot Butte are prominent examples.