It begins from a nondescript spot on Highway 50, where a creek and a social trail lead up into a forested canyon, and then the rocky south slope of the mountain. It is a tenaciously direct line to the top, gaining more than 4,000 vertical feet in about 3 miles.
To find the trail, park at a shoulder turnout on the north side of Highway 50, about 100 yards west and downhill of a gravel chain-up area on the opposite side of the road, near mile marker 59. The turnout is located at 38.807133, -120.138127. From there, walk just past the chain-up area where a small creek flows under the road. Look for a faint trail near the creek and take this into the forest.
The path might be hard to follow at first, but it becomes more obvious as you get higher in the canyon and near treeline. In general, follow the main drainage up the canyon. At about 8,500 feet elevation you will break out of the forest and onto Pyramid’s broad south ridgeline. Punch straight up this, over talus and through stunted spruce and pine, to finally reach the lofty summit. Enjoy immense views over all of the Desolation Wilderness, with its many water-filled granite basins, bald summits, and snowfields. The southeast edge of Lake Tahoe can be seen in the distance beyond Mount Tallac, with the Carson Range as a backdrop.
Sources:
https://www.summitpost.org/pyramid-peak/151024
https://www.summitpost.org/rocky-canyon-se-ridge/156730