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: There will be a modest fee (TBA) to cover the guidebook, snacks, beverages, and lunches.
Students: Thanks to an Ivanhoe Electric sponsorship, students who are current student members with both AGS and AIPG can register free for this trip and receive other benefits to be announced.
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.
Registration: Registration will open for all on this site at a later date. Keep watch. An announcement will be sent out to members of both AGS and AIPG when registration goes live. At this point, we do not anticipate a limit on the number of participants, but there will be a deadline five (5) 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. Suggestions include Majestic Mountain Inn, Best Western, Quality Inn, and Comfort Inn. The casino at the south end of town has a large hotel (Mazatzal Casino)
Note 1: 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.
Note 2: We are currently making arrangements for blocks of rooms at group rates at several of the above named hotels. Please stay tuned to this space.
