From the foothills north of the Beartooth Mountains, Pyramid Mountain appears as a high, prominant, pointed peak with fairly low angle sides. The easiest route can be considered as about class 2-3, but because of its positioning and the lack of nearby trails, it likely sees probably less that ten people a year. The most challenging part about this mountain is that it begins with a 3000 ft climb out of the valley to the Fishtail Plateau, and then finishes with about 4-5 miles of hiking and scrambling above the treeline. Total gain is greater that 6000 vertical feet.
To get to the base of the mountain, drive up the West Rosebud Canyon (the same one often used for Granite Peak climbs), and park somewhere around the Emerald Lake Campground. To begin the climb, begin up the northwest side of the valley.
Another way to possibly approach may be from the Benbow Road, which turns off at the town of Dean and winds and switchbacks up into the West Fishtail Creek drainage. I have not tried a route this way, so I can't give anymore clues at this time. In fact, I am not even sure if this way would work very well. If you want an adventure, try it out and let us know.
To get to the West Rosebud, if you are coming from Bozeman or Billings along I-90, turn of at Columbus and make your way through town and jump on highway 78 south. Continue to follow that through Absarokee, and then turn right at the junction with the gas station about 3 miles south of Absarokee. Proceed along the highway through Fishtail and then, about a mile out of town when the road takes a turn to the west, turn left on to the narrow, paved road. (note that if you continue along the highway here, you will end up in Dean, where the turn off for the other possible route beginning is located.) Follow that road and turn off just before it turns to gravel onto the gravel road that heads down across the river, and on up into the canyon.
To get to the West Rosebud from Red Lodge, take highway 78 out of town and follow it for about 18-20 miles. You will then come down off of a big hill and in the trees at the bottom, you will find the town named Roscoe. (note that even though the highway travels directly past this town, it is notoriously difficult to find. In fact, there are shirts and bumper stickers out there with the phrase "Where the hell is Roscoe?" printed on them.) If you find roscoe, turn off there and follow the street through the middle of town and on out of town. Just out of town, the road will turn to gravel and fork, at which point you will want to take the right fork. Follow that road until you pop out on a narrow, paved road, and then turn left and follow it up the hill. Continue along this paved road and turn off on to the gravel road that goes down across the river and up into the West Rosebud. (note that the turnoff is just before the narrow, paved road turns to gravel. )
As with the other Beartooth Peaks, there are no permits or fees, and the West Rosebud road is passable for basically all of the year. If you try the Benbow Road approach, deep snows will probably not allow vehicle passage from late fall through early summer.
When To Climb
The easiest time of the year to climb Pyramid mountain is from about mid-July to mid-September. With considerable snow on the ground, this could turn into quite an arduous journey, especially the section of the climb up to above the timberline.
There are two campgrounds in the West Rosebud Canyon, and one of them, called the Emerald Lake Campground, is right at the base of the climb. There are fees at the campgrounds that I believe are around $6-8 a night. You can also camp along the climb, but most of the ways to the top will offer basically no water. I recommend this climb as a long day hike after staying the night at the Emerald Lake campground.
The most accurate forcasts for Pyramid mountain that I know of would be those for the nearby town of Red Lodge. You can also call the Beartooth ranger station at (406) 446-2103.