Rio Grande del Norte National Monument features the deepest canyon in New Mexico at its Wild Rivers Recreation Area. The Rio Grande River is continuously carving this gorge into the Taos Plateau, a dry plain dotted with extinct volcanoes. The cutting of the canyon began when a vast Ice Age lake in Colorado spilled over about 440,000 years ago.

The Taos Plateau itself forms the floor of the Rio Grande rift valley, flanked by mountain ranges both east and west. Like the East African rift valley, famous as the home of early humans, the rift is a place where the Earth's crust is pulling apart.

Join Rock on Mother Earth for a hike into the gorge with two rangers, and an interview with the lead author of a recent study of its geology.

----more----Podcast chapters (M= minutes, S= seconds) are summarized here:

0M 0S OPENING: The Rio Grande is continuously carving New Mexico’s deepest canyon into the Taos Plateau, a dry plain dotted with extinct volcanoes. Join me for a walk with two rangers (Tim Long and James Larson) and an interview with the lead researcher of a 2019 study on Wild Rivers geology (Travis Clow).

0M 50S RIO GRANDE RIFT: Ranger Long uses a wood block model to illustrate Earth’s crust pulling apart along the Rio Grande Rift. The Sangre de Cristo and Tusas mountains rise up on the flanks of the Taos Plateau, while magma rising from Earth’s mantle spills out as lava that mingles with sediments eroded from the mountains.

6M 56S PAY STATION VIEWPOINT: A 2017 U.S. Geological Survey guidebook in hand, I visit a gorge overlook to examine a “columnar-jointed” lava flow and a vista that includes numerous volcanoes, plus 25-million-year-old volcanic rocks uplifted in a fault block.

12M 34S LA JUNTA POINT: Ranger Larson describes the view of the gorge and surroundings. Ranger Long shows how water availability in the canyon creates an “inverted ecosystem.” He recounts the beginnings of the canyon, believed to have resulted about 400,000 years ago from the spillover of a vast Ice Age lake in Colorado.

17M 54S TERRACES: Dr. Clow talks about phases of canyon-deepening (incision) and floodplain formation (aggradation) that have alternated since the spillover event. He describes his research to obtain the age of remnants of former floodplains, called terraces. The results suggest that melting after glacial episodes coincided with incision.

27M 35S INTO THE GORGE: I give an overview of the round trip to the bottom of the gorge that Ranger Larson led me on. Then I describe beginning the hike with views to the north. Next, Dr. Clow explains the origin of piles of boulders (talus) eroded from the rim’s cliffs.

30M 33S TOREVA BLOCKS: An area shaded by Ponderosa Pine nestles just upslope of a tilted strip of lava rock, twice the length of a football field. Dr. Clow describes how this “Toreva block” slid down from the cliffs above without shattering into smaller pieces.

33M 48S TO THE RIO GRANDE: The rangers and I meet hikers Sue and Dudley Chelton, a couple just past their 50th wedding anniversary, who share their delight at having visited the river’s edge. Ranger Long talks about the role of water in an arid landscape.

38M 30S ROCK ART: Ranger Larson leads me, along with Floridians Kristi Lowery and Jason Buchheim, to some extraordinary petroglyphs. Dr. Clow tells the geology of the boulders that First Peoples chose to decorate.

45M 57S NEXT EPISODE, THANKS: I close by promising Episode 3 and thanking participants.

Sources: https://www.blm.gov/visit/rgdnnm ; https://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/3/820/4701037/820.pdf; https://pubs.usgs.gov/sir/2017/5022/r/sir20175022r.pdf