sedona

Field Guide – Oak Creek-Mormon Lake Graben Northern Arizona

The Oak Creek-Mormon Lake Graben lies between Flagstaff and Sedona, Arizona. The Arizona Geological Society and geologist Paul A. Lindberg have produced a 13-page field guide to the geology of the area (shown on the map below).

This geologic field trip guide circumnavigates a loop of ~120 miles from Flagstaff to Sedona along Highway 89A and returns to Flagstaff along the Lake Mary Road. The guide contains many illustrations and photographs and may be downloaded from:
http://tinyurl.com/AGS-Spring2015-Fieldtrip

Lindberg introduces us to the local geological setting:

“The Oak Creek-Mormon Lake graben (a rift valley formed by extension of the earth’s crust) has been faulted into the southwestern margin of the Colorado Plateau as basin and range crustal extension has migrated eastward across Western U.S. over time. The graben may be as young as 2-3 million years old, based upon the youthful appearance of numerous V-shaped canyons (Oak Creek, West Fork, Munds, Woods and Rattlesnake Canyons) that cut the minimally eroded original surface of the largely basalt covered core of the graben. That morphology is in sharp contrast to more maturely eroded landforms along the northeast margin of 10 Ma Verde graben near Sedona. Timing of the genesis of the Oak Creek-Mormon Lake graben may be contemporaneous with the main eruptive cycle of San Francisco Peaks north of Flagstaff, Arizona.”

The 12 geologic stops focus on recent faulting and the encroachment of Basin and Range extensional structures on the Colorado Plateau. Each stop is detailed in the text, which is amply illustrated with photographs and colored geologic sketches.

Oak Creek Graben map

A guide to the geology of the Sedona & Oak Creek Canyon area of Arizona

DTE-20 cover

UPDATE NOV 2016: This booklet is now available for free download:

 http://repository.azgs.az.gov/uri_gin/azgs/dlio/1694

This 40-page booklet, published by the Arizona Geological Survey, is one of the Survey’s “Down To Earth” series (DTE-20). A list of the other publications in this series is at the bottom of this post. The DTE series is written in non-technical terms for people who have an interest in geology, but may not have had formal training. The goal is to provide the reader with an understanding of dynamic processes that form various geological features. This issue will be of interest to professional geologists as well because it tells you where to find neat stuff. I found the booklet very interesting and a good refresher.

This publication has a two page introduction to the region describing the geological history, one of deserts, beaches, volcanic flows, uplift, and faulting. This is followed by descriptions of 24 “features.” Each feature has a great photograph and text explaining how it was formed. (See example page below.)

All of the features in this edition can be reached by short walks from Highways 89A and 79, Road 78, and from U.S. Forest Service roads. A map is provided near the front of the booklet. The back cover shows a stratigraphic column and a note by the author, Dr. John V. Bezy.

This booklet costs $8.95 and may be ordered from the Arizona Geological Survey, 416 W. Congress St. Suite 100., Tucson, AZ 85701 (order form here). Phone 520-770-3500, email: store@azgs.az.gov.

Other publications in the Down To Earth series:

DTE-20 feature13

DTE-1 Energy Resources of Arizona, by J.T. Duncan and F.P. Mancini, 1991, 17 p., scale 1:1,000,000. $6.50

DTE-2 Radon Gas: A Geologic Hazard in Arizona, by J.E. Spencer, 1992, 17 p. $2.50

DTE-3 Land Subsidence and Earth Fissures in Arizona, by S. Slaff, 1993, 24 p. $5.00

DTE-4 How Geologists Tell Time, by E.M. VandenDolder, 1995, 33 p. online at azgs.az.gov

DTE-5 ‘Things Geologic’, A Collection of Writings by H. Wesley Peirce, complied and edited by Robin Frisch-Gleason, 1996, 39 p. $8.00

DTE-6 Ice Age Mammals of the San Pedro River Valley Southeastern Arizona, by A.W. Amann, Jr., J.V. Bezy, R. Ratkevich, W.M. Witkind, 1997, 19 p. $6.95

DTE-7 Highlights of Northern Arizona Geology, compiled and edited by Robin Frisch-Gleason, 1998, 44 p. $7.95

DTE-9 A Guide to the Geology of Organ Pipe Cactus National Monument and the Pinacate Biosphere Reserve, by J.V. Bezy, J.T. Gutmann, and G.B. Haxel, 2000, 63 p. $7.95

DTE-10 Guide to Geologic Features at Petrified Forest National Park , by J.V. Bezy and A.S. Trevena, 2000, 48 p. $6.95

DTE-11 Rocks in the Chiricahua National Monument and the Fort Bowie National Historic Site, by J.V. Bezy, 2001, 48 p. $7.95

DTE-12 A Guide to the Geology of Catalina State Park and the Western Santa Catalina Mountains, by J.V. Bezy, 2002, 48 p. $7.95

DTE-13 A Home Buyer’s Guide to Geologic Hazards in Arizona, by R.C. Harris and P.A. Pearthree, 2002, 36 p. $8.95

DTE-14 A Guide to the Geology of the Flagstaff area, by J.V. Bezy, 2003, 56 p. $7.95

DTE-15 Roadside Geology: Wupatki and Sunset Crater Volcano National Monument, by S. L. Hanson 2003, 32 p. $6.95

DTE-16 A Guide to the Geology of the White Mountains and the Springerville Volcanic Field, Arizona, by J. V. Bezy and A. S. Trevena, 2003, 56 p. $7.95

DTE-17 A Guide to the Geology of Sabino Canyon and the Catalina Highway, by J.V. Bezy, 2004, 45 p. $7.95

DTE 18 A Guide to the Geology of Saguaro National Park, by J.V. Bezy, 2005, 36p. $7.95

DTE-19 A Geologic and Natural History Tour through Nevada and Arizona along U.S. Highway 93, by Joseph V. Tingly, Kris A Pizarro, Christopher Ross, and Phillip Pearthree, 2010, $27.95

See also my posts:

Arizona Geologic History: Chapter 1, Precambrian Time When Arizona was at the South Pole

Arizona Geological History: Chapter 2, Cambrian and Ordovician Time

Arizona Geological History: Chapter 3: Devonian to Permian Time

Arizona Geological History Chapter 4: Triassic Period

Arizona Geological History Chapter 5: Jurassic Time

Arizona Geological History 6, The Cretaceous Period

Arizona Geological History 7: The Cenozoic Era

Sedona’s Sinkholes

The City of Sedona is surrounded by seven sinkholes. That is the subject of a new report by geologist Paul Lindberg published by the Arizona Geological Survey.  The spectacular red rock country near Sedona, Arizona, hides an unusual and potentially hazardous geologic feature.

DevilsKitchenSinkhole

Sinkholes are collapse features that form when surface, and near-surface rocks subside into the cavernous Redwall Limestone, which lies more than 600 feet below the surface. Gradual collapse of the roof of the cave results in a breccia pipe that extends upward from the Redwall Limestone to the floor of the sinkhole, situated up to 100 feet, below the exposed rim of the sinkhole. See cross-section below.

The Devils Kitchen sinkhole is the most active of the seven, with historic collapses in the 1880s, 1989, and 1995. The other sinkholes are in various stages of collapse, some beginning as early as the end of the last ice age, about 10,000-years ago. Structures like this on the north rim of the Grand Canyon host uranium deposits.

Sinkhole-Xsection

The following graphic (from the Devil’s Canyon report, cited below) shows how sinkholes develop.

Sinkholestoping

The Sedona sinkholes range in size from about 225 feet in diameter by 100 feet deep at Red Canyon, to Sinkhole 4543, which is 13 feet in diameter and about 3 feet deep. Devils Kitchen, the most well known of the sinkholes, has an opening 150 feet by 90 feet, with the floor situated 35 to 70 feet below the rim. Lindberg estimates that caverns in the Redwall Limestone, could have volumes on the order of 1.3 million cubic feet (a cave roughly 100 feet high and 130 feet in diameter).

According to the report, the groundwater of the Middle Verde watershed, which fills the Redwall caverns, began as precipitation on the Colorado Plateau, near the western flank of the San Francisco Peaks above 6,900 feet. Groundwater passes beneath Sedona at a flow rate of approximately 15 million gallons per day.

Sinkhole-arcuate

Lindberg notes, “While the danger of future collapse is minimal to humans, unregulated septic leakage into hidden sinkhole breccias within the town limits could contaminate groundwater being tapped for municipal use ….” A second hazard, which could threaten hikers and sightseers, are the presence of sandstone overhangs at several sinkholes that could collapse without warning in the near future.

The arcuate patterns as shown in the photo above represent a place where the rock has been stressed enough to break, but the rock has not yet collapsed. This may be the site of a future sinkhole.

(I wonder if arcuate patterns such as shown above might have given rise to the legend of vortexes near Sedona?)

Lindberg’s reports include pictures, maps, and schematic, to-scale drawings of each sinkhole. A pdf copy of the full report is available at the Geological Survey’s publications page in the Contributed Reports section: http://www.azgs.az.gov/publications_online.shtml

The general report on Sedona sinkholes (21 Mb) can be downloaded from:

http://www.azgs.az.gov/publications_online/contributed_reports/cr10c.pdf

A report specific to the Devil’s Canyon sinkhole (24 Mb) can be downloaded from :

http://www.azgs.az.gov/publications_online/contributed_reports/cr10b.pdf