New Mexico’s El Malpais Lava Beds at I-40 — © Dave Spier
East of Grants, New Mexico (USA), Interstate 40 passes through the north end of the El Malpais lava fields. (Malpais is Spanish for “badlands” and was used by early map makers to describe volcanic terrain.) The area is related to the Zuni-Bandera volcanic field. Of the numerous basalt flows, two reached the present I-40/Rt. 124 highways. The youngest, the McCarty flow, is a mere thousand years old. Stop at the mile 93 rest areas for a closer look or drive Rt. 124 parallel to the interstate. The older Calderon flow reached to Grants and can be accessed from the exits. The small volcanoes at the source are 20-30 miles southwest in El Malpais National Monument which is reached by Routes 117 and 53.
On Google Earth 6.2, you can zoom in on I-40 between Grants and McCarty’s to the southeast. (Exit 89 GPS co-ords are 35° 05′ 04.82″ N, 107° 46′ 12.77″ W) The geologically “recent” McCarty’s lava flow is an irregular black line heading north along the west side of Rt. 117 at the base of the Las Ventanas Ridge, then widening and “pooling” east of exit 89 (where Rt. 117 begins at I-40), then streaming east-southeast along Rt. 124 (Historic Rt. 66) most of the way to McCarty’s. The dissected north rim of the McCarty’s Mesa is south of Rt. 124 and formed the southern barrier constraining the lava. The older Calderon lava flow is an irregular brownish-gray blob west of exit 89 on the Google aerial view.
The basalt is similar to the dark lava flows that form the Moon’s “seas.”
Roadside Geology of New Mexico, by Halka Chronic (© 1987/reprinted 2005), published by Mountain Press
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