The older sedimentary rocks were intruded (invaded) by a molten mass of magma deep in the earths crust approximately 35 million years ago. These rocks, called the Alta Stock, have the classic granitic salt and pepper texture and are compositionally a granodiorite, an igneous rock similar to granite but with more calcium, iron and magnesium.
| The Alta Stock underlies all of Mt. Wolverine, Patsy Marley and most of the Crooked Mile. The top of the Collins chair is visible in the lower left corner of the picture. Photo taken looking east from the east ridge on Mt. Baldy. |
| Close up of the granodiorite in Albion Basin. |