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GSA THOMPSON FIELD FORUM
14–21 September 2019
Age and Carving of Grand Canyon: Toward a Resolution of 150 Years of Debate
An eight-day, 280-mile field conference by raft through the Grand Canyon, USA.
CONVENERS, AFFILIATIONS, AND TOPICS
Karl Karlstrom, University of New Mexico (Grand Canyon
geology and tectonics)
Laura Crossey, University of New Mexico (hydrochemistry,
mantle-to-groundwater)
Eugene Humphreys, University of Oregon (Colorado Plateau,
geodynamics)
David Shuster, University of California Berkeley
(thermochronology)
Kelin Whipple, Arizona State University (geomorphology)
The age and evolution of the 1.6-km-deep, 270-mile-long
Grand Canyon have been debated since J.W. Powell’s exploration
of the Colorado River in 1869. This GSA Thompson Field Forum
honors the 150th anniversary of Powell’s trip. It will involve 28
researchers and young scientists who will discuss the evidence
for the age and incision history of Grand Canyon in the context
of recent advances and ongoing debates. The objective is to pro-
mote a next generation of research on the evolution and tectonic
geomorphology of this iconic region, as well as similar studies
globally, and debate the evidence for and against mantle-driven
dynamic topography. The field forum will start and end in Las
Vegas, Nevada, USA, and will be run under a charter with Grand
Canyon Expeditions (https://www.gcex.com/motorized/). Rigor-
ous hiking is planned.
Objectives
This Thompson Field Forum will build on synergistic land
sessions to showcase field research advances and remaining
research questions in this iconic field laboratory. Karl Karlstrom
and Laura Crossey will coordinate field stops and discussions
of incision data, neotectonics, and lava dam studies. Eugene
Humphreys will coordinate geodynamics discussions to debate
the hypothesis for mantle-driven uplift of the Colorado Plateau–
Rocky Mountain region. David Shuster will coordinate discus-
sions of thermochronologic studies of now-eroded landscapes.
Kelin Whipple will coordinate geomorphology discussions of
bedrock strength controls on river and canyon morphology and
debate evidence for steady versus transient incision.
This research has global reverberations in terms of Cenozoic
neotectonics, landscape evolution, and mantle-driven dynamic to-
pography. The objective is to stimulate next steps on these topics.
20 GSA Today | August 2018
Description
River trips allow several types of interactive sessions:
(1) discussions on the outcrop; (2) “plenary” discussions at morn-
ing and evening seminars; and (3) short talks and discussions on
boats while floating past key areas. Each participant will be asked
ahead of time to prepare and lead a seminar or outcrop discus-
sion, with poster-type materials to hold up or pass out. The eight-
day river trip covers 280 miles from Lees Ferry to Pearce Ferry
such that there is also ample time for one-on-one and small-group
informal discussion as we travel downriver. Distance is measured
in river miles (RM) downstream from Lees Ferry. On average,
we cover about 35 RM per day (four hours per day of motoring
through spectacular geology). Numerous hour-long to half-day
hikes are planned. Key half-day hikes may be dated strath-to-
strath incision history locations at Kwagunt, Palisadea, and Elves
Chasm; high terraces near Unkar Rapids; travertines on Tonto
Platform near Hermit Creek; dated landslide river diversions
near Deer Creek Falls; and lava dam dates and incision points in
western Grand Canyon.
Logistics
The trip will be run by commercial charter rafting company
Grand Canyon Expeditions. Participants arrive in Las Vegas, Ne-
vada, USA, on Friday, 13 Sept., in time for an evening orientation
meeting at 7 p.m. An early start with a bus takes us to Lees Ferry
for a midday launch on 14 Sept. Camping gear, dry bags, and
life jackets are provided to participants. The trip will take out at
Pearce Ferry midday on Saturday, 21 Sept., and participants are
bused to Las Vegas. Grand Canyon Expeditions uses a jet boat to
pick up participants at Separation Canyon (RM 240), which al-
lows more rapid boat transit across the abrupt boundary between
the Colorado Plateau and Basin and Range provinces at RM 270
enroute to the take out at RM 280 and discuss the “Muddy Creek
constraint.” There will be a final get together that evening, but
many participants may want to proceed to Phoenix (a 1.5-hour
flight) to check in for the GSA Annual Meeting icebreaker.
Preliminary Agenda
13 Sept.: Arrive in Las Vegas; group orientation at Residence Inn
Las Vegas Hughes Center (hotel covered in trip cost);
14 Sept.: Bus to Lees Ferry and launch midday;