Geology and Fossils of Mesa Prieta


Geology and Fossils of Mesa Prieta

   *Tuesday, July 28th, 2015, 6:30 – 8:30 pm at Historic Los Luceros, Alcalde, NM. Suggested donation – $5

Lecture by Scott Aby

ALCALDE – Like many mesas in New Mexico, Black Mesa is topped by a thin layer of lava, which is resistant to erosion. That is why these mesas stand high in the landscape – because everything else has eroded away around them. The lava on Black Mesa is between three and four million years old, and is a type of lava that flows easily, usually down valleys. In Mesa Prieta‚Äôs case, we know that the bottom of the valley was at the top of the mesa when that lava was erupted. This type of lava (called Basalt), gets a coating on it called “desert varnish” after a few million years. Petroglyphs are made by chipping the varnish off the rocks to reveal the lighter colored “fresh” rock underneath.   
Black Mesa is interesting to geologists because of the well-exposed sediments beneath that has fossils of “savannah type” mammals in them. These include camels, horses, rhinos, ground sloths, elephants, giant tortoises and a whole bunch of other animals. These fossils may represent some of the first open grassland environments in Earth’s history. The American Museum of Natural History collected many fossils from this area between 1920-1960 and ongoing projects with the BLM and New Mexico Museum of Natural history are adding to these collections.

About Scott Aby

Scott Aby has been making maps and collecting fossils in northern New Mexico professionally for the last thirteen years.  He has worked for the USGS, planted trees for the forest service, and peeled quite a few vigas. Scott has a Bachelors degree from Humboldt State University in Northern California, where he studied local geology.  Scott has a Masters degree in geology from UNM where he studied faults and stream terraces in the Jemez Mountains.