ON THE ROCKS Presents

South Park Basin

August 14-15, 2026

Trip Leader: Peter Barkmann (CGS), Marieke Dechesne (CGS),  and Ned Sterne

Trip Coordinator: Ralf Topper and Laura Wray

Trip Description

Randy Marsh Might Know South Park but … Its Geologic Setting and Evolution is the Domain of Our Trip Leaders

Join Peter Barkmann (CGS-retired), Marieke Dechesne (USGS), and Ned Sterne as they present the complex geologic setting and long history of sedimentation and tectonic deformation that is South Park in a 2-day RMAG On-The-Rocks field trip scheduled for August 14^th & 15^th.

Whether your bent is history, stratigraphy, structure, tectonic and landscape evolution, glaciology, hydrology, hydrocarbon exploration or all of the above, this is the trip for you. Recent mapping efforts and hydrocarbon exploration have brought to light the magnitude in complexity of a structural basin recognized for its unique sedimentary and tectonic setting.

This field trip through one of Colorado's scenic gems will examine how Paleozoic, Mesozoic, and Cenozoic strata record the tectonic signatures of at least three orogenic episodes. We will cross the Elkhorn–Williams Range thrust system into the structural block caught between Laramide uplifts preserving synorogenic sediments from the Pennsylvanian-Permian ancestral Rocky Mountain tectonic episode in juxtaposition with synorogenic sediments from the subsequent Laramide tectonic episode. We’ll discuss the:

1) folded and faulted late Cretaceous marine sediments from the Western Interior Seaway that are recent targets for petroleum exploration;

2) evidence of evaporitic tectonism originating from Pennsylvanian evaporite deposits;

3) the progression of Laramide deformation and synorogenic sedimentation;

4) explore post-Laramide rift-related features; and

5) view many varied features in the Pleistocene glacial landscape.

Lodging has been reserved for Friday night at the Hartsel Ranch (www.hartselranch.co), which offers lodge rooms, shared cabins, and camping opportunities.  Trip leaders will conduct a presentation in the main lodge on Friday evening after dinner with refreshments provided by RMAG.

The group will meet at the Kenosha Pass scenic overlook along US highway 285 at 8:30 am. Denver area attendees will meet at 7:30 am at the Twin Forks Park n Ride on highway 285 for carpooling. Attendees need to wear suitable shoes/boots for short walks through native vegetation/landcover, uneven terrain and moderate hills. Appropriate clothes for possible changes in the weather are also advised including rain gear, sun hat, sunscreen, and insect repellant. 

The field trip will end back at the Kenosha Pass scenic overlook by approximately 4:30 pm on Saturday.

Lodging & Meals

Lodging reservations are to be make directly with the Hartsel Ranch at (336)-706-5923. Please reference that you are with RMAG. Cost for rooms is $200 plus tax (lodge rooms have king or queen beds and private en suite full bathrooms). Cabins have one or more bedrooms with full kitchen, full bathroom, living room, fireplace, and front porch. Camping cost is $30 per person with bathroom and shower facilities available. Group meals are also provided for a fee with Friday night dinner ($45) consisting of grilled chicken and beef, potatoes au gratin, green beans, salad, rolls, and desert. Saturday morning breakfast ($20) consists of breakfast burritos, baked goods, fruit, coffee/tea, and juice. Special dietary needs can be accommodated. Payment for lodging and meals are to be made directly to the Hartsel Ranch at the time of reservation.

Attendees are responsible to bring their own lunch for Friday and Saturday and drinks/water during the day. Prepackaged refrigerated food and drinks are available at the Hartsel quick stop.

Cost

• $100 for members
• $130 for non-members. (not a member? click here to join)
• Are you a student? email staff@rmag.org

Registration

Registration Closes August 10, 2026. 

Refunds for the August 14-15th, trip are only available until August 3, 2026

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 Waiver and Release of Liability and Medical Emergency Form. Those who fail to complete these form will not be permitted to attend the field trip.