The Blanca Massif is also Precambrian rock, while most of the rest of the Sangres is composed of younger Permian-Pennsylvanian (about 250-million-year-old) rock, a mix of sedimentary conglomerates, silty mudstones and shales, sandstones, limestone beds and igneous intrusions. These sedimentary rocks originated as sediment eroded from the Ancestral Rocky Mountains. Crestone Conglomerate are a feature on many of the peaks, including Crestone Needle. The conglomerate settled near the uplift and contains boulders as large as 6 feet in diameter.
