2012
Fifty miles north of Albuquerque, just north of the junction of U.S. #550 & NM #4, begins the Southern end of the Jemez Mountain Range, which roughly parallels the North-South Sangre de Cristo Mountains 20 miles further east.
Between these mountain ranges lies the Río Grande Rift, into which all surrounding runoff flows, creating the Rio Grande River that originates in the San Juan Mountains in southern Colorado and flows all the way south across the Mexican border.
The small town of San Ysidro is situated at the southern end of the Jemez Mountains, where the Jemez river flows south from the Valles Caldera, joining the Río Grande about half-way to Albuquerque.
San Ysidro is the intersection of four significant geologic features: the Colorado Plateau to the west, the 75 million-year-old Sierra Nacimiento uplift to the north, the Río Grande rift to the east, and the northeast-trending Sierra Jemez lineament, characterized by its young volcanism cutting across all three geologic provinces. The 15 million-year-old Jemez volcanic field is visible to the northeast; the 2 to 3 million-year-old Cabezon Peak is located just to the west. 3.3 million-year-old Mt. Taylor can be seen on the skyline to the west. The surrounding hills are covered with sedimentary red to green siltstones and mudstones, similar to the Painted Desert’s petrified forest Chinle group, deposited on the floodplain of a large west-to-northwest river system some 210 million years ago.
In addition to the red and green stone from the petrified forest, San Ysidro has numerous interesting anticlines and synclines — reflecting the movement of earth structures formed by geological folding.
