Unlike the rest of the San Juan Mountains, which are volcanic in origin, the Needle Mountains (along with the Grenadier Range) are a mass of uplifted Precambrian rocks. They consist chiefly of quartzite, granite, and amphibolite. The mountains are referred to as the Needle Mountains Uplift.[2][3]
^Barker, Fred (1969). "A brief geological history of the Precambrian rocks of the Needle Mountains, southwestern Colorado". In Shomaker, J.W. (ed.). San Juan, San Miguel, La Plata Region (New Mexico and Colorado). Fall field conference guidebook ; 19. New Mexico Geological Society. pp. 148–149.