The Cochiti Formation is a geologic unit near the southwest Jemez Mountains in northern New Mexico that preserves sediment eroded from Keres Group volcanic highlands and deposited in nearby basins between about 10 and 2.6 million years ago, from the middle Miocene into the Pliocene. In its refined definition, it includes only volcanic-derived sedimentary strata south of the Jemez Mountains that rest on older Keres rocks and are overlain by younger gravels. A notable subdivision, the Lookout Park Gravel Member, helps date the youngest part of the sequence. The formation remains important for reconstructing erosion, deposition, and landscape change along the southern edge of the Jemez volcanic field.