The main tributaries streams that join to form the Jemez River are San Antonio Creek and the East Fork Jemez River. Both originate on the west side of the Sierra de los Valles near the northwest corner of Los Alamos County. San Antonio Creek flows west in a northward curve, through Valle Toledo and Valle San Antonio. The East Fork Jemez River flows west in a southward curve, through Valle Grande. These valleys are all part of the Valles Caldera. The two tributary streams join near Battleship Rock in Cañon de San Diego, forming the Jemez River's main stem.