PRE-MEETING FIELD TRIP

(DENVER to CRESTONE)

MAY 30, 2016

The Pre-Meeting Field Trip (morning of Monday, May 30) travels from the  Best Western Plus Airport hotel near the Denver International Airport (top right) to Crestone (bottom center). The trip provides transport to Crestone for those Registrants who do not wish to rent a car in Denver or travel to Crestone by other means. The Field Trip bus will leave from the Best Western Plus Airport hotel on Tower Road at 8 am. Estimated arrival time in Crestone is 1 pm.

Fig. 1. Google Earth map of the route (blue) of the Pre-Meeting Field Trip from the Denver International Airport (upper right) to Crestone (bottom center). Red lines show major Quaternary normal faults of the Rio Grande Rift.

Fig. 1. Google Earth map of the route (blue) of the Pre-Meeting Field Trip from the Denver International Airport (upper right) to Crestone (bottom center). Red lines show major Quaternary normal faults of the Rio Grande Rift.

The Field Trip traverses four different geologic terrains: the Colorado Piedmont, the Front Range, South Park, and the Rio Grande Rift.

The first segment travels west across metropolitan Denver which lies on the Colorado Piedmont geomorphic province, and the structural Denver Basin of late Cretaceous age. The Colorado Piedmont is home to 80% of Colorado’s 5.4 million residents. To the west you will see the escarpment of the Front Range, which rises from elevations of 1600 m to 2500 m. To the east, the Great Plains stretch 2000 km to the Mississippi River lowlands.

From the Piedmont we turn west into the Colorado Front Range on US Highway 285, crossing the upturned stratigraphic section at the western edge of the Denver Basin. The Front Range is a Precambrian-cored basement uplift formed mainly in the late Cretaceous Laramide Orogeny of east-west compression. On our route we mainly travel on a 20-30 km-wide dissected Tertiary erosion surface cut on Precambrian basement rocks, with the high peaks of the Front Range (>4000 m) visible to the west.

Fig. 2. Google Earth image of our route from the Denver Basin to South Park via US 285. The high peaks of the Front Range lie in the upper right.

Fig. 2. Google Earth image of our route from the Denver Basin to South Park via US 285. The high peaks of the Front Range lie in the upper right.

South Park (of American cartoon fame) is a 40 km-wide, 70 km-long, treeless intermontane basin lying at 2700 m elevation, surrounded by mountains up to 4300 m high. Due to the harsh climate and preponderance of fine-grained Paleozoic and Mesozoic rocks, it is a grassland. The buffalo roam there, and the deer and antelope play (Fig. 3).

South Park cartoon sign CLIP

Fig. 3. Top, the most famous residents of South Park; Bottom, American Bison (often called “buffalo”) graze in South Park.

Fig. 3. Top, the most famous residents of South Park; Bottom, American Bison (often called “buffalo”) graze in South Park.

The final segment travels south down the axis of the Rio Grande Rift from Buena Vista to Crestone. At Buena Vista in the Upper Arkansas Valley part of the Rift, the rift floor lies at 2400 m and the flanking hosts to 4300 m (Fig. 4). Our route takes us south over Poncha Pass (2746 m) and into the San Luis Valley, the largest graben of the Rio Grande Rift.

Fig. 4. Mount Princeton (top center; elevation 4327 m) rises above the floor of the Rio Grande Rift, and the town of Buena Vista and Upper Arkansas River (elevation 2400 m). Fault scarps lie hidden in the forest at the base of range.

Fig. 4. Mount Princeton (top center; elevation 4327 m) rises above the floor of the Rio Grande Rift, and the town of Buena Vista and Upper Arkansas River (elevation 2400 m). Fault scarps lie hidden in the forest at the base of range.