The Sierra Nacimiento (official name), or Nacimiento Mountains, are a mountain range in the northwestern part of the U.S. state of New Mexico. They are just west of the more prominent Jemez Mountains near the town of Cuba, and are separated from them by the Río Guadalupe and the Río de Las Vacas. This article will consider them as a unit together with the San Pedro Mountains, which are a smaller range contiguous with the Sierra Nacimiento on the north, and which are also part of the Nacimiento Uplift and lie at the edge of the greater San Juan Basin, which sits atop the Colorado Plateau. The combined range runs almost due north-south with a length of about 40 mi (65 km).