AGS–AIPG Fall Field-Trip
October 24-25, 2026
Paleozoic seaways, islands, and stratigraphy along the Mogollon Rim
Trip Leaders: Peter Dohms (AIPG CPG and retired consulting geologist who lives in Payson), will lead the field trip on Saturday. Stephen J. Reynolds** (ASU School of Earth and Space Exploration, Presidents Professor Emeritus), Julia K. Johnson** (ASU School of Earth and Space Exploration, Teaching Professor Emeritus), and Chad Kwiatkowski (Research Geologist, Arizona Geological Survey and AGS Member) will lead the field trip on Sunday.
Where: Payson, AZ; approx 5000' el. (Tonto Natural Bridge State Park and surroundings)
Cost: $30 to cover the guidebook, snacks, beverages, and lunches. Registration is online by credit card. Note: if you allow the option for your name to be visible to public, your local friends will be able to find you and organize car pools (parking may be limited at some stops).
Students: Ivanhoe Electric is sponsoring students for this trip. In order to qualify for FREE student registration, you must register as a student with AGS (this website, free). We strongly encourage all students to register with AIPG (aipg.org, also free for students). Both organizations have geological networking benefits. Student members will also be eligible to receive other benefits to be announced. AGS thanks Ivanhoe Electric for this sponsorship.
Liability Waviers: Attendees must sign liability waivers for both AGS and AIPG. AGS: Click here for Liability Wavier. AIPG: TBA Completed copies of these form will be collected at the beginning of the field trip.
Goals and Itinerary
The goals of this joint AGS–AIPG field trip are to explore the geology of the central part of the Mogollon Rim and nearby geologic features between Pine and Forest Lakes. The trip will focus on the Proterozoic basement rocks and their influence on the subsequent deposition of Paleozoic units, including onlap of these units onto a persistent, positive feature known as Pine Island. The trip will also examine aspects of the Pennsylvanian and Permian stratigraphy as revealed by a recent major stratigraphic study conducted by two of the field-trip leaders. We will also examine other interesting features, such as the beautiful travertine natural bridge at Tonto Natural Bridge State Park, and sinkholes.
Day 1 (9:30AM to 5:00PM), with three stops, all north of Payson, will explore the concept that erosionally resistant Proterozoic rocks formed emergent features that rose above the shallow seas during deposition of sediments in Paleozoic time. Previous authors (Conway, et al, 2008; Weitzman, 2002) have noted the presence of Paleozoic sediments deposited upon ("draped over") Proterozoic Haigler Rhyolite and quartzites of the Mazatzal Group, but they did not fully explore the implications of those observations. Opinions will be sought among trip participants.
Day 2, (8:00AM to 4:00PM) with stops east of Payson, will examine the Pennsylvania and Permian stratigraphy of the Mogollon Rim in the context of a major stratigraphic revision, whose field work has been completed and whose results are currently mostly written up for publication in a memoir. This research has been conducted by Spencer Lucas of the New Mexico Museum of Natural History, Stephen Reynolds and Julia Johnson, both emeritus professors at ASU, William DeMichele, of the Smithsonian Natural History Museum, and others. We will explore the Paleozoic sequence from the Devonian through the Permian to allow participants to see the characteristics of the main formations, including the Devonian Martin Formation, Mississippian Redwall limestone, Pennsylvanian units that have traditionally been called the Naco Formation, and redbeds of the Supai Group. Trip leaders will present the results of abundant new paleontologic data that indicates that the lower part of the Supai is Pennsylvanian in age and that some widely quoted correlations are incorrect. We will discuss our proposed new nomenclature of the Pennsylvanian and Permian rocks. ** Steve and Julia are co-authors of the new Roadside Geology of Arizona book (2nd Edition), with "great photos and discussions of their entire field-trip route." Bring your copy for them to sign or buy one from them on Sunday ($30 cash or check).
Registration: Registration is open for all. At this point, we do not anticipate a limit on the number of participants, but the deadline to register is October 20, four (4) days before the start of the trip to give us numbers and time for guidebook printing and food and beverage purchases.
Lodging: Motel stays are not included in price and are the responsibility of attendees. There are plenty of motels in Payson. Recommendations include Majestic Mountain Inn, Best Western, Quality Inn, and Comfort Inn. We are working on getting group rates at these motels for Saturday night with an option for Friday night at the same rate. Magestic Mountain (928.474.0185) has agreed hold several rooms at a group rate of $99 + tax (add $20-$25 for final rate). Best Western (928.474.9800) has agreed to hold another block of rooms at the following rate: single King bed (2 people max) for $129.99 + tax, double queen bed for $149.99 + tax (2 people, extra adults up to 4 max for additional $20/adult). Mention AGS or AIPG (or geology field trip) to get these rooms and rates. I haven't been able to reach the correct person for Quality Inn ((928.474.3241) or Comfort Inn (928.472.7484), but you can get a good rate if you use a loyalty card (probably true for the BW too). All four of these hotels have outer parking where we can leave cars for the day in order to car pool. The casino at the south end of town also has a large hotel (Mazatzal Casino).
Driving and Car Pooling: The 1st stop on Saturday (9:30 AM, with time to sign and collect waiver forms) is roughly 2 hours from Phoenix and Flagstaff, and roughly 4 hours from Tucson. Some participants may want to reserve rooms for both Friday and Saturday nights to in order to enjoy a more leisurely Saturday morning. Car pooling locations for those driving long distances may be announced via email to those already registered and/or on this site at a later date.
