American Institute of Professional Geologists
Arizona Section Newsletter
Walter Heinrichs, Jr.
We received just a brief note that Walter E. Heinrichs, Jr., CPG-688, one of Arizona's best known mining geologists, passed away on Thursday, October 10, 2013.
Photo of Lee Allison presenting the Arizona Geological Society's Honorary Lifetime Membership to Walt in 2008.
Arizona Section Field Trips
The Arizona Section hosted the Fall 2013 field trip in northern Arizona on Saturday, October 5th. Section member Paul Lindberg (CPG-06344) prepared the 9-page color guidebook and road log, and led 21 participants on the field trip. The trip circumnavigated the northern portion of what is probably one of the youngest Basin and Range grabens to cut the Mogollon Rim. The Oak Creek - Mormon Lake Graben is a Pliocene-age (2 to 3Ma) structure identified by Paul during his many years of exploring and geologic mapping of the area south of Flagstaff and east of Sedona.
The field trip made a counter-clockwise tour around the northern end of the graben to study faults, rock exposures, fault outcrops, and other physical features related to rift valley genesis. We first visited a fault scarp within the graben that has been breached by an active stream channel that drains the Munds Park area. The next stop was a viewpoint on Interstate 17 that afforded a view to the west of Jacks Canyon fault that is the southward continuation of the Oak Creek fault - the west graben boundary. Traveling south and then east, we stopped to look at Stoneman Lake, a nearly mile-wide, roughly circular depression in the graben. The origin of the depression is uncertain; it may be a small graben within the graben, or an area of basalt collapse into a lava tube.
The trip continued to Mormon Lake, where another viewpoint afforded a panoramic view of the east side of the Mormon Lake depression, which forms the eastern boundary of the graben. Paul discussed the drainage changes that resulted from the crustal stretching of this part of the continent. The next stop was at a spectacular hands-on fault scarp where down-dropped Miocene basalt lava on the west side of the fault is in contact with Permian Kaibab Limestone on the east side of the fault (Photograph #1).
Photograph #1: Fault scarp along east boundary of Oak Creek – Mormon Lake graben
The tour then passed through the southern side of Flagstaff, which lies within the shallow northern part of the graben. Then we headed south into Oak Creek Canyon to observe two ages of fault movement along the Oak Creek fault zone. One phase is Laramide age (~70 Ma) compression where high-angle reverse faulting raised the east side of Oak Creek Canyon. Evidence for this phase included fault drag on the west side of the fault zone visible along Oak Creek (Photograph #2). The much younger (2 to 3 Ma) superimposed reactivation of the modern normal phase of the Oak Creek fault dropped the east side back down. Evidence for this phase included younger basalt on the east side of the fault juxtaposed against older (Permian) sedimentary rocks, and bleaching of the normally red sandstones by fluids migrating along the fault zone.
Photograph #2: Fault drag is down-to-the west on opposite bank of north to south flowing Oak Creek. Fault is behind the photographer.
Then we drove up Airport Mesa in Sedona for an aerial view of the Sedona area (Photograph #3). Paul pointed out the difference in erosional character between the now-dry stream-cut valleys in the Sedona area, and the young V-shaped Oak Creek Canyon and other smaller canyons that drain off the graben. We left Airport Mesa traveling south on Highway 179 and made two additional stops to look at graben-related features. One unanswered question was the true origin of the “exotic gravels, Beavertail Gravels, and Rim Gravels” that are present in the study area. Previous workers suggested the gravels are different units that were deposited from north-to-south off the rim. Paul’s studies suggest the gravels are correlative as one unit with a common source, and were transported from south to north. The highlands source was eroded away prior to formation of the graben. Local outcrops are now observed stair-stepping down to the south as a result of formation of the graben.
Photograph #3: Sedona area viewed from Airport Mesa northward
At each field trip stop, we had a lively discussion on the geology of the area. Paul noted that additional work needs to be done in the area to firm up some of his interpretations, including a few more basalt age-dates to clarify the stratigraphic and structural relationships. Anyone need a thesis topic?
Thank you to Paul Lindberg for another great field trip.
- Arizona Section - Oak Creek - Mormon Lake Graben - October 2013
- Arizona Section “Golden Anniversary” Trip to Chihuahua, Mexico - April 2013
- AZ Fall Field Trip - 10/22/11
- AIPG Field Trip - May 2011
- AIPG Field Trip - October 2010
- AIPG Arizona Field Trip - May 22
- Arizona 2009 Field Tour to Sonora, Mexico
Arizona Section Officers
Doug Bartlett, CPG-08433
2014 President, AIPG Arizona Section
Clear Creek Associates
6155 E. Indian School Rd., Suite 200
Scottsdale, AZ 85251
480-659-7131 or firstname.lastname@example.org
Dawn Garcia, CPG-08313
2014 President, AIPG Arizona Section
JDS Energy & Mining
2015 West River Road, Suite 151
Tucson, AZ 85704
520-789-7606 ext 109 or DawnG@jdsmining.ca
Julie M. Hamilton, CPG-09428
2014 President Elect, AIPG Arizona Section
1405 W. Auto Drive
Tempe, AZ 85284
480-940-2320 or Julie.Hamilton@amec.com
James Adu, MEM-1311
2014 Secretary, AIPG Arizona Section
Freeport-McMoRan Sierrita Operations
6200 W. Duval Mine Rd.
Green Valley, AZ 85614
520-393-2669 or James_Adu@fmi.com
Jeff Cornoyer, MEM-02174
2014 Treasurer, AIPG Arizona Section
9420 E. Golf Links Rd., Suite 108
Tucson, AZ 85730
520-604-0503 or email@example.com