Johnson Peak is made of eroded granite. At 85 Ma, the Johnson Granite Porphyry is the youngest granite rock in the Yosemite National Park, though the entire peak formed beneath the Earth's crust. It broached the surface much later, via subduction.[3]
R.B. Marshall named Johnson Peak, in the 1890s, to honor a teamster and guide in his survey party, with Professor Davidson. They also climbed Mount Conness.[3]
Johnson granite porphyry, whose name derives from Johnson Peak, is found there.[5] Far above what is now Johnson Peak, it is possible that a volcanic caldera once may have existed.[6][7]
^"PRISM Climate Group, Oregon State University". PRISM Climate Group, Oregon State University. Retrieved October 8, 2023. To find the table data on the PRISM website, start by clicking Coordinates (under Location); copy Latitude and Longitude figures from top of table; click Zoom to location; click Precipitation, Minimum temp, Mean temp, Maximum temp; click 30-year normals, 1991-2020; click 800m; click Retrieve Time Series button.