| Pentagon Mountain | |
| Elevation Ft: | 8873 |
| Elevation Ref: | [1] |
| Prominence Ft: | 1353 |
| Isolation Mi: | 10.86 |
| Isolation Ref: | [2] |
| Parent Peak: | Three Sisters, North (8,900 ft) |
| Location: | Flathead County, Montana, U.S. |
| Map: | Montana#USA |
| Relief: | 1 |
| Label Position: | right |
| Range: | Rocky Mountains Flathead Range Trilobite Range |
| Coordinates: | 47.9273°N -113.1248°W |
| Topo: | USGS Pentagon Mountain |
| Rock: | Sedimentary rock |
| Age: | Precambrian |
Pentagon Mountain is an 8873abbr=offNaNabbr=off mountain summit located in Flathead County of the U.S. state of Montana.[3]
Pentagon Mountain is the highest point in the Trilobite Range, which is a subset of the Flathead Range.[1] It is set within the Bob Marshall Wilderness, on land managed by Flathead National Forest. It is situated two miles west of the Continental Divide, and topographic relief is significant as the summit rises approximately 3000abbr=offNaNabbr=off above Pentagon Creek in approximately one mile. Precipitation runoff from the mountain drains west and south to the Spotted Bear River via Pentagon Creek, and north to the Middle Fork Flathead River via Clack Creek. The nearest higher neighbor is Three Sisters, 10.56miles to the south.[1]
Based on the Köppen climate classification, Pentagon Mountain is located in a subarctic climate zone characterized by long, usually very cold winters, and short, cool to mild summers.[4] Winter temperatures can drop below −10 °F with wind chill factors below −30 °F.
Pentagon Mountain is composed of sedimentary rock laid down during the Precambrian to Jurassic periods. Formed in shallow seas, this sedimentary rock was initially uplifted beginning 170 million years ago when the Lewis Overthrust fault pushed an enormous slab of precambrian rocks 31NaN1 thick, 50miles wide and 160miles long over younger rock of the cretaceous period.[5]