Day 1 Grants to Dos Lomas to San Mateo Mesa
Bonnie Frey, Shari Kelley, Kate Zeigler, and Virginia McLemore

Summary:

We will spend Day 1 of this field conference within the sedimentary strata that surround Mt. Taylor, starting in the Jurassic Entrada Sandstone and ending in the Upper Cretaceous Point Lookout Sandstone (Fig. 1.1). The van caravan will embark from Grants and progress west along I–40, then east past Haystack Mountain via NM–122 and Haystack Road (County Road–23). At the intersection of CR–23 with NM–605, the caravan will turn north and travel through the San Mateo Creek basin, west of Mt. Taylor, and toward the end of the day will turn to the east toward Mt. Taylor and the village of San Mateo. If we make it to the Optional Stop 5, we will progress to the Menefee Formation and introduce some of the volcanic rocks associated with Mt. Taylor.

Remnants of the uranium mining industry dot the landscape of our route, including former and existing mine sites and four mill sites. We have included several mini-papers by or about people who played a role in this history, and we will learn about some of the recent research and remediation activities in the area.

The day will start with a trek from Grants to Haystack Road, named for the now famous Haystack Mountain where a discovery of uranium purportedly started the 1950s boom in the area. We will make our way east to Stop 1, where we will view the contact between the Entrada Sandstone and the Todilto Limestone (both Jurassic). We will discuss the formation of unusual mound structures and other fold-like features in the Todilto, observe the transition from the more “crinkly” upper bedding to the lower platy bedding, and discover some of the less prominent, small-scale textures.

From there, the group will drive east along the Mesa Montañosa to Stop 2, where we will hike from the vehicles to the base of the mesa. The hike will take us along an arroyo to the bottom of the Bluff Sandstone (where we may get a very limited glimpse of the Summerville Formation), past a faulted outcrop, and up to the Morrison Formation, where we will point out the Recapture, Westwater Canyon and Brushy Basin members.

Once back on the road, we will progress along NM–605 and NM–509 into Ambrosia Lake country and past two inactive mill sites. Stop 3 will be at the field trailer of Rio Algom Mining LLC, where we will talk about the uranium mill sites, mining history, and some of the recent research on uranium geochemistry.

Stop 4 will involve a short walking tour along the edge of San Mateo Mesa, passing through the Cretaceous Gibson Coal Member of Crevasse Canyon Formation and the Hosta Tongue of the Point Lookout Sandstone. Participants will be asked to examine these deposits carefully, because on Day 2 the group will compare these rocks to Cretaceous outcrops in the Amphitheater of Mt. Taylor.

If time allows, we will travel to the east slope of La Cuchilla Canyon to look at the contact of the Menefee Formation with the 3.3 Ma Grants Ridge rhyolite tuff. This optional stop, Stop 5, will serve to introduce the volcanics of Mt. Taylor, which we will discuss in more depth on Day 2.


Note: The full-text of all Fall Field Conference road logs are only available in print.


Citation:

  1. Frey, Bonnie; Kelley, Shari; Zeigler, Kate; McLemore, Virginia, 2021, Day 1 Grants to Dos Lomas to San Mateo Mesa, in: New Mexico Geological Society, 71st Annual Fall Field Conference, September 2021, Geology of Mount Taylor, Frey, Bonnie A.; Kelley, Shari A.; Zeigler, Kate E.; McLemore, Virginia T.; Goff, Fraser; Ulmer-Scholle, Dana S., New Mexico Geological Society, Guidebook, pp. 1-22.

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