Valle Grande

The panel's figures have been refined since it went up. The caldera's collapse is now dated to about 1.23 million years ago, and the youngest of the domes it describes, Banco Bonito in the preserve's southwest, erupted about 69,000 years ago rather than 50,000. The geothermal promise did not hold. Union Oil began drilling the field beneath Redondo Peak in 1959, a 50-megawatt plant was proposed in 1977 with federal backing, and when deeper wells failed to add enough steam the project ended in January 1982 without producing electricity.

What the plaque says

Official Scenic Historic Marker Valle Grande About one million years ago, the magnificent valley before you was formed by collapse, after a series of tremendous volcanic eruptions ejected a Volume of material more than 500 times greater than the May 1980 eruptions of Mt. St Helens, This event climaxed more than 13 million years of volcanism in the Jemez Mountains. Minor volumes of magma, leaking to the surface as recently as 50,000 years ago, formed the dome-like hills between you and the skyline to the north, which is the opposite wall of the enormous Valles Caldera. The heat from young volcanism makes this area attractive for geothermal energy.

Where it stands

Worth the stop nearby

• Valles Caldera National Preserve — 1.8 mi
  A crater thirteen miles across, floored with grass, left by an eruption 1.25 million years ago and owned privately for 140 years under a law that called it vacant land.
• Fuller Lodge — 9.0 mi
  The upright-log dining hall of a boys' ranch school, which fed and housed the Manhattan Project after the Army bought the school in 1942.
• Bandelier National Monument — 12 mi
  Rooms carved into soft volcanic tuff in Frijoles Canyon, named for a Swiss scholar who was led there in 1880 by a man from Cochiti Pueblo.
• Jemez Historic Site — 14 mi
  The stone walls of a 1620s mission church standing among the ruins of Gisewa, a Jemez village named for the hot springs beside it.

More markers nearby

• Peggy Pond Church — 8.8 mi
• Los Alamos — 12 mi
• Jémez State Monument — 14 mi
• Women of Cochiti — 17 mi