Intermountain Region

Grouse peak is a piece of the crater rim that has not moved much (14 miles northeast of Challis in Lost River Range). The slope behind Challis Hot Spring is a conglomerate breccia that is part of the ejecta blanket. Look for shatter cones in Belt and Lemhi rocks.

The Beaverhead Impact Structure is one of only eight known bolide impacts with craters over 50 km in diameter. Scientists now believe that the center of the Beaverhead Impact Crater is in Idaho within the Salmon-Challis National Forest.  It is 60 km in diameter and the impact is estimated to have occurred about 900 million years ago.  Tectonism has broken up regions of the original shocked rocks and dispersed them as large discrete areas across the geological landscape.  Direct evidence for the structure is found at Island Butte in the southern Beaverhead Mountains, Montana where shatter cones and shocked grains are found in Mesoproterozoic sandstone, and the underlying Archean gneiss contains pseudotachylite dikes and pods (injection breccias emplaced in fractures during meteoric impact). (see Carr and Link, 1999)

The trailhead is located near the Bighorn Crags campground. From Challis, drive 9 miles north on Highway 93 to the Morgan Creek Road turnoff. (on the left) Follow this pavement/gravel road for 20 miles to the Morgan Creek Summit where it becomes the Panther Creek Road. Follow this road another 14 miles to the signed turn-off at Porphyry Creek. Follow the Porphyry Creek Road 6 miles to a four way intersection. Turn right at this intersection on Forest Road 114. There will be another intersection with the road to Yellowjacket Lake. Bear right continuing on road 114 past the Crags campground to the trailhead.

Most prominent in the Salmon River Range are the Bighorn Crags, located in the Frank Church River of No Return Wilderness. The Bighorn Crags feature the most spectacular peaks and lakes in the wilderness. The scenery includes craggy granite spires, high peaks, and dozens of gorgeous alpine lakes tucked into glacial cirques. The Bighorn Crags are Eocene granitic rocks intruded into Eocene volcanic rocks of the Challis volcanic group.