The Jemez River is a tributary of the Rio Grande in eastern Sandoval County, New Mexico, United States. The river is formed by the confluence of the East Fork Jemez River and San Antonio Creek, which drain a number of tributaries in the area of the Jemez Mountains and Santa Fe National Forest. The Jemez River is about 50 miles long, or about 8…The Jemez River is a tributary of the Rio Grande in eastern Sandoval County, New Mexico, United States. The river is formed by the confluence of the East Fork Jemez River and San Antonio Creek, which drain a number of tributaries in the area of the Jemez Mountains and Santa Fe National Forest. The Jemez River is about 50 miles long, or about 80 miles long if its longest headwater tributary, San Antonio Creek, is included. The East Fork Jemez River is about 22 miles long. Both San Antonio Creek and the East Fork Jemez River flow through intricate meanders along their courses. The East Fork Jemez is a National Wild and Scenic River.