Invasion of the Magmatic Dikes - Big Bend NP, TX

Black circle: Dodson Trail, towards Elephant Tusk, in the Chisos Mountains of Big Bend N.P., TX

(From https://www.usgs.gov/media/images/big-bend-geologic-map)

Invasion of the shallow sea: locate Texas on the map. Here's the late Cretaceous (135-100 Ma) setting for deposition of sediments in Big Bend, which then uplifted during volcanic activity related to _,46-28 Ma.
(From http://www.scotese.com/cretaceo.htm)

Andesites, rhyolites, trachyandesites, tuffs and basalts. Underlying Cretaceous sediments tilted during volcanic activity, then dusted with ash clouds, basalt flows.
(From https://www.researchgate.net/figure/Generalized-volcanic-stratigraphy-of-western-Big-Bend-National-Park-following-Miggins-et_fig2_254990352)

A walk along the Dodson trail reveals... vertical dikes, limestone seeps dotted with happy ferns, and petrified elephant tusks jutting 5,249 feet into the sky. 

Mile 1: Facing west towards uncommon red beds- "related to the Emory Peak Rhyolite member of the South Rim Formation" (http://prism-redfern.org/bbvirtualtrip/bluecreek/bluecreek.html), Cretaceous sediments to the right.

Crow's perspective of red outcrops (bottom right) seen along Dodson trail.

Mile 1.5: Seep within a limestone formation.

Dike trending NE-SW with Elephant Tusk (Tertiary granitic intrusion) to the SE (view southeast).


View SW from South Rim - dikes from the Glenn Springs intrusion (2). The "more dikes" are pictured closer-up in previous photo.

View SW. Tortuga mountains made of Cretaceous Aguja fm, "upper Cretaceous Aguj formaiton, "in whose sediments you see the transition from sea to land in Big Bend" (redfern).

Shale-like strata en route Boquillas hot springs = Boquillas formation (1). Deposited 135 Ma as shallow Cretaceous sea, which retreated 100 Ma- watch for clams, snails in the Boquillas.

South Rim geochem https://gsa.confex.com/gsa/2005SE/finalprogram/abstract_83339.htm
Dikes http://prism-redfern.org/bbvirtualtrip/rim/rim.html

1. https://www.nps.gov/bibe/learn/nature/geology.htm
2. History and geology https://www.nps.gov/parkhistory/online_books/geology/publications/state/tx/1968-7/sec2.htm 

chisos mtns quadrangle https://pubs.usgs.gov/sim/3140/downloads/pdf/SIM_3140.pdf
big bend geo map https://pubs.usgs.gov/sim/3142/downloads/pdf/SIM3142map_hi-res.pdf
useful blog http://prism-redfern.org/bbvirtualtrip/dodson/dodson.html