GEOLOGY OF
THE JEMEZ MOUNTAINSby Dr. Charles R. Mansfield The Jemez mountains are the remnant of a series of
major volcanic eruptions that occurred about one million years ago. The volcanic activity in the
Jemez complex probably began in the Eocene era and has continued to about 50,000 years ago. Redondo
Peak, nearly 12,000 feet above sea level, is a remnant of the original peak. The peaks on the rim of
the caldera are between 10,000 and 11,000 feet above sea level. The eruptions of 1 million years ago ejected around 100 cubic miles of ash leaving a caldera 20 miles across. The tuff deposits on the outside of the caldera are nearly 1000 feet deep in some places. Erosion has cut steep canyons through the tuff. These canyons include Frijoles, Water, Valle, Pueblo, Los Alamos, Guaje and Santa Clara. Small streams are found in some of these canyons. The tuff deposits on the eastern edge of the Caldera are called the Pajarito (Little Bird) Plateau. The Pajarito plateau slopes gently downward to the East toward the Rio Grande river at a rate of about 1.5%. The Rio Grande river, near Los Alamos, is at an elevation of about 5500 ft above sea level. |
