The Manzano Mountains are the southern part of a larger geologic unit known as the Sandia-Manzano Mountains, which are an east-tilted fault-block range forming part of the eastern edge of the Albuquerque Basin in the Rio Grande rift. They are separated from the Sandia Mountains to the north by the Manzanitas Mountains and Tijeras Canyon. Both the Manzano and Sandia mountains are capped by Paleozoic sedimentary rocks, with Proterozoic metamorphic rocks making up most of the mountains' steep western faces. These include the Sevilleta metarhyolite, with an age of 1665 ±16 Ma.