Geotour of Verde River, Central ARIZONA

Joe Cook, first author of Verde River maps and report, wading across the Verde River, holding a GPS receiver in his right hand.

In 2010, AZGS geoscientists led by Joe Cook and Phil Pearthree mapped a two-mile swath centered on the 175 mile course of the Verde River.  They distinguished geologically-young  river channel, terrace and overbank sediments (materials deposited over the past 10,000 years) from older river deposits.

To make this work palatable to non-geologists, we present GeoTour of the Verde River.  This online, interactive map service displays the geologic mapping in a Google maps environment – as you zoom in, the map fills the screen.  To help viewers visualize the geologic setting and the different map units, we included a suite of 41 photographs, stretching from the spring-fed headwaters of the Verde to its lower sandy reaches near Fountain Hills.

Verde River
Geologic Photo Tour






Besides the recent river deposits, AZGS geoscientists encountered, and mapped, other geologic units, including: Pleistocene river deposits (deposits laid down between 11,600-years- and 2.6 million-years- ago), Tertiary basalts, and from the upper and middle reaches, Paleozoic rocks formed between 270 and 525 million years before the present: Kaibab, Toroweap, Coconino, Schnebly Hills, Hermit, Supai, Redwall, Martin, and Tapeats Formations.  Sparse outcrops of even older granitic rocks occur along the lower reaches of the Verde River.

Location of Verde River, central Arizona, and recently published geologic strip maps of Holocene-age river deposits.

Geology is all about sediments, minerals,  rocks, and the processes, such as running water, that shape the Earth’s surface.  When coupled with climate and elevation, geology --  the composition and distribution of Earth material -- exerts control over the makeup of biological communities, including those that inhabit riparian zones. 

The Verde riparian zone is a greenbelt of desert willow, Arizona ash, boxelder, red willow, cottonwood, sycamore, and the occasional tamarisk,  and is home to some of the finest birdwatching in the Southwestern U.S.  Populations of great blue herons, great egrets, snowy egrets, white-faced ibis, green-backed herons, violet green swallows, white throated swifts, southwestern willow flycatchers, bald eagles, peregrine falcons, ospreys, and a wide variety of hawks and songbirds feed and nest along the Verde and its tributaries. 

The photographic atlas that accompanies “GeoTour of the Verde River” shows geologic units, ranging from the youngest Holocene sediments -- channel gravels to the fine clays and silts of overbank deposits – 300- to 500-million-year-old limestones, sandstones, and shales.

The observant eye may detect patterns in vegetation distribution, too. For instance, along frequently inundated cobbly deposits of the lower Verde, desert broom and tamarisk are common. Higher standing silty to sandy Holocene river deposits frequently host dense mesquite bosques. Even further removed from the modern floodplain, clay and carbonate-rich Pleistocene river terraces are studded with saguaro, prickly pear and agave.    

The Verde River geologic maps should prove invaluable to local communities, farmers, conservationists, environmentalists, and federal and state land management authorities who share the responsibility for maintaining a sustainable natural resource. For a full citation, see the New Publications section. 

The maps and report are available online at AZGS Online Publications .   To order printed copies or the GIS geodatabase and shape files call 520.770.3500 (fax 520.770.3505). 

 




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