ON THE ROCKS Presents

LOWER San Juan river raft trip with flow (Fort Lewis on the Water)

June 4-8

Trip Leader: Dr. Gary Gianniny, Fort Lewis College

Come join the RMAG for five days and four nights on the lower San Juan River. Traveling with renowned geologists Dr Gary Gianniny (Fort Lewis College) and Dr Rip Langford (University of Texas at El Paso), and rafting professionals from Fort Lewis on the Water program, we will enter the Glen Canyon National Recreation Area and float through goosenecks carved deep into the sedimentary section to experience dramatic geology, fabulous outcrops, and world-class hiking opportunities.

Trip Description:

The lower San Juan River exposes the Pennsylvanian Hermosa Group, deposited on the stable, broad, shallow shelf near the western margin of the Paradox Basin.  Lithologies outcropping along the river are outcrop analogs for producing intervals at the giant Aneth Oil Field, satellite fields in the Paradox Basin, and at Barker Dome & Ute Dome fields on the Four Corners Platform.  Geologists rafting through these folded Pennsylvanian strata can examine phylloid algal and microbial bioherms (oil and gas reservoirs), and organic-rich black shales (source rocks).   Higher up in the section, cross-bedded carbonate grainstones appear in the younger Honaker Trail Formation, followed upwards by non-marine terrigenous sediments in the Permian Lower Cutler Group, including rare rhizolith channel-fill conglomerates  Spectacular exposures of the overlying Cedar Mesa Sandstone provide a superb view of the complex facies of a mixed wet eolian and fluvial system. 

Day 1

Meeting in Durango, CO, the group will ride the three hours (in FLC/FLOW vans) to Mexican Hat, Utah for 10am launch at RM (River Mile) 26.6, then quickly enter the 14-mile series of goosenecks, where the San Juan River meanders at the bottom of deep, almost vertical cliffs while nearly doubling back on itself.  Day One float starts in the axis of the Mexican Hat Syncline, near exposures of the shallowest productive sandstone in the Pennsylvanian Honaker Trail Sandstone in the Mexican Hat Oil Field, then floats thru the entire exposed Pennsylvanian stratigraphic section, ending near the axis of the Cedar Mesa Anticline.  On Day 1 we will also hike across the Mendenhall Meander (~200ft, <2mi) while the boats float around to meet us on the other side.  We will see Pennsylvanian microbial/Chaetetes bioherms, incised valleys, current-aligned stromatolites, and eolian-delivered lowstand clastic deposits.  

Tentative Camp: Honaker Trail, RM 44

Day 2

Day 2 begins with an optional (highly recommended) hike to the canyon rim on the Honaker Trail before getting back in the boats and navigating through a few small rapids.  The hike up the Honaker Trail (2-1/2mi, ~1250ft elevation gain) to the canyon rim provides hands-on opportunity to examine the entire Pennsylvanian stratigraphic section, including correlative equivalents of all the productive carbonate cycles of the Paradox Formation.  Downstream we will see oil seeps, many stacked microbial bioherms, bioherm-inherited topography focusing subsequent clastic-filled incised valleys, and anomalous coarse-grained basement-derived clastics along the lowest Paradox Formation sequence set boundary at the Atokan/Desmoinesian contact.   

Tentative Camp: above or at John’s Canyon, RM 56-58

Day 3

On Day 3 we will run Government Rapid (Class III), the biggest rapid on the San Juan River.  As the river continues to drop structurally toward the Colorado River, westward dip of the of the rocks increases, and the river climbs rapidly stratigraphically into progressively younger rocks as it descends.  An afternoon hike is planned up from our campsite up Slickhorn Canyon to observe an abandoned/historic exploration dry hole and the Pennsylvanian marine (Honaker Trail Formation) to Permian fluvial/eolian (Cedar Mesa Sandstone) transition.

Reserved Camp: Slickhorn Canyon, RM 66.8

Day 4

On Day 4 we will float up section thru the top of Pennsylvanian Honaker Trail Formation, Permian Halgaito Formation, and Cedar Mesa Sandstone.  We will cap Day 4 with a hike up Oljeto Canyon from our campsite, where we will examine non-marine eolian & interdune deposits of the Cedar Mesa Sandstone.  On Day 4 we will also examine modern aggraded deposits of the San Juan River, reflecting base-level changes recorded in response to the building of Glen Canyon Dam and the creation of Lake Powell.

Reserved Camp: Oljeto Canyon, RM 76

Day 5

On the final morning we will float the calm remainder to the takeout at Clay Hills Crossing.  As we descend toward the level of Lake Powell, much of the Permian plunges back into the subsurface.  By the time we leave the river at Clay Hills Crossing, the San Juan River canyon has down-cut to the top of the Permian Cedar Mesa Sandstone, upon which we will begin our drive back to Durango.  NOTE that vans will be returning to Durango by an alternate route that does not pass thru Bluff or Mexican Hat, so riding in FLC/FLOW vans is highly recommended

Cost

• $1400 for members

• $1500 for non-members (not a member? click here to join)

Registration Closes May 26, 2023. 

Refunds for the June 4-8th trip are only available until May 10, 2023. 

If you are unable to attend, your registration for all RMAG events are transferable. RMAG members may transfer their registration to another RMAG member, and non-members can transfer their registrations to whomever they wish. Should an RMAG member wish to transfer their registration to a non-member, the non-member would need to pay the balance between the member and non-member price.

Waivers

All registrants must fill out the Medical, Emergency, Waiver and Release of Liability form. Those who fail to complete the form will not be permitted to attend the field trip.