Ice Age Española

The great glaciers of the Pleistocene were more real in Michigan where I grew up than they are in the Española valley. As a child I imagined a great blanket of snow called Illinois sidling over my neighborhood, then retreating, only to reappear in a few thousand years as the Wisconsin glacier.

Archaeologists today don’t mention glacial episodes for sites that weren’t under ice. They prefer to use the marine isotope stages developed by Cesare Emiliani and Nicholas Shackleton. The MIS numbers demarcate variations in ice composition that occurred when expanding glaciers monopolized the lighter oxygen isotopes in water, leaving the heavier ones in sea beds. Even MIS numbers are cold periods, odd numbers warm.

[Click on table to enlarge]

The stages have the advantage of avoiding labels specific to Europe and North America and help define relationships between the different ice sheets. In New Mexico, the Bull Lake glacier occurred during the Illinois in the northeast and the Riss in Europe. The ice was centered in northwestern Montana and reached down to the San Juan mountains in southern Colorado.

The later Pinedale coincided with the Wisconsin and the European Würm. It’s icecap rested on the Yellowstone Plateau, but it left glacial lakes in the Sangre de Cristo: Katherine and Nambé near Santa Fé Baldy, Horseshoe in the headwaters of the Red River.

Scott Renbarger believed the trees blown down near Trailrider Wall were growing in a moraine. Ponderosa pine roots reach deep when there’s no surface water, but only go 3' down in water-retentive soils. Rocks can trap water to create undemanding environments.

Abandoning the names of glaciers obscures the fact their affects were felt far away. When glaciers were expanding they absorbed water that otherwise would have fallen as rain. Areas beyond the ice fields dried. Winds blew their dust against mountains, grinding rock surfaces into particles that fell into great dune fields. The Great Plains and the rich farm lands of the Danube River valley began as Pleistocene aeolian deposits.

Stephen Hall said the dominant species in San Juan County and the Chuska Mountains during cold spells were piñon and Ponderosa pine. Limber pine also grew in San Juan County. Sagebrush grew in the warmer periods called interglacials. In those millennia, water was released, lakes formed, and rivers were swollen by rain.

In the Española valley the released waters sometimes brought down boulders that temporarily blocked White Rock Canyon. Then floods formed wetlands that filled existing lowlands and left a deceptively level surface. When the waters receded, they left behind badlands that border the eastern valley.

The badlands east of Llano Road between the high school and the Santa Cruz cemetery are fingers of fine-grained sand, siltstone and sandstone. Daniel Koning suspected they "may possibly lie near the north edge of a former playa or lake."

Farther north, east of San Juan Pueblo, rocks from the Middle to Upper Pleistocene have been judged 50,000 to 300,000 years old. About 25 to 40% of the pebbles are cobble sized. A bit south toward the casino, there are fewer cobbles, 10 to 30%. The "light yellowish brown to very pale brown pebbly sand" contains some quartzite. Sitting atop the eastern badlands, wind driven sand remains.

Notes: Quotations are from one of the two Koning reports below. They can be downloaded from the New Mexico Bureau of Geology and Mineral Resources website under the tabs for Publications/Maps/Geologic Maps. Locations are from the maps.

Hall, Stephen A. "Ice Age Vegetation and Flora of New Mexico," in S. G. Lucas, G. S. Morgan, and K. E. Zeigler, New Mexico’s Ice Ages, 2005.

Koning, Daniel J. Preliminary Geologic Map of the Española Quadrangle, Rio Arriba and Santa Fe Counties, New Mexico, 2002, map and report.

_____ and Kim Manley. Geologic Map of the San Juan Pueblo Quadrangle, Rio Arriba and Santa Fe Counties, New Mexico, 2003, map and report.

Oliver, William W. and Russell A. Ryker. "Pinus ponderosa Dougl. Ex Laws," in Russell M. Burns and Barbara H. Honkala, Silvics of North America, Volume 1, 1990.

Renbarger, Scott. "A Glacial Moraine in the Rio en Medio Watershed," Geological Joy in New Mexico, 23 July 2013. If you want to learn more about glaciers in the Sangre, he includes some wonderful pictures with his blog post.

Photographs:
1. Sagebrush, Taos Plateau with gorge in distance, 11 December 2011.

2. Badlands east of Llano Road between Santa Cruz cemetery and Española high school, 22
April 2015.

3. Badlands east of San Juan pueblo, seen from route 68 looking east, 20 May 2015.