Sedona: Red Rock - Secret Mountain Wilderness - Geology

Sedona is located on the edge of the Mogollon Rim (pronounced Muggey-own,) a steep escarpment on the southwest edge of the Colorado Plateau.

It runs approximately 300 miles from northern Yavapai County southeast to the White Mountains and New Mexico border.

The extraordinary landscape we see today predates the rim's uplift, a story that begins 300 million years ago when Sedona was located on a submerged coastline near the equator.

This period gave rise to the Redwall Limestone layer, the lowest exposed strata in the modern Sedona region.

Redwall Limestone is 300 - 600' thick and ranges from gray to dark brown in color. Small ancient sea creatures such as snails, trilobites, brachiopods, mollusks and fish can be found in this layer.

Over the next 30 million years this land was exposed by a receding sea and subjected to erosion. Rivers carried silt and mud from distant mountains in the north, while lapping waves deposited sand to form the Supai Group layers.

Supai covers the Redwall Limestone layer and is about 200 - 600' thick. Shale, siltstone, mudstone, stratified quartz, conglomerates and various sandstones comprise this group:

• Esplanade Formation (sandstone)


• Wescogame Formation (sandstone)


• Manakacha Formation (cross-stratified quartz and sandstone)


• Watahomigi Formation (limestone over sandstone, and mudstone)

Most significantly, the Redwall Limestone and Supai groups hold iron minerals that absorbed oxygen, which oxidizes (effectively rusting) to produce the rich red hues for which Sedona is famous.

About 270 million years ago additional waves of shale, mudstone, siltstone and sandstone were carried by river systems from the Ancestral Rocky Mountains that drained into floodplains in the Sedona region.

This created a 300' thick layer of red rock is called the Hermit Formation. Modern Sedona lies near the top of the Hermit Formation. The Hermit Foundation was subsequently by covered by sand dunes, followed by the shallow vestiges of the Pedragosa Sea.

The mass of the Pedragosa Sea flattened underlying rock layers that now appear as light colored, horizontal ripples in rock (e.g. on Bear Mountain).

The sea's ebb and flow also deposited a 10 - 30' grayish limestone layer called the Fort Apache Member. As the sea retreated, dunes once again blew in and covered the area.

The Hermit Foundation, ancient sand dunes and Fort Apache Member were eventually aggregated and compressed into horizontal layers of the Schnebly Hill Formation - the primary constituent of Sedona's Red Rock Country.

The Schnebly Hill Formation is about 1,000' thick, with the Bell Rock sublayer near the bottom, Fort Apache in the middle and Sycamore Pass sublayer on top.

As the inland Pedregosa Sea made its final retreat about 270 million years ago, new dunes amassed that were eventually compressed into a 500 - 1000' thick layer of Coconino Sandstone.

The two most predominant rock layers in Sedona are Schnebly Hill and Coconino Sandstone. Schnebly Hill Sandstone is comprised of mostly red rocks on the bottom portion of cliffs, capped by Coconino Sandstone, which is cream-yellow.

Red rock layers formed by the presence of oceans is generally replaced by lighter colored rock at higher elevations where deserts and dunes settled after their final retreat.

The Kaibab Sea gradually enveloped the Sedona area about 260 million years ago, whose ebb and flow deposited a variety of sediments such as limestone (deeper water) and sandstone (shallower water).

These alternating layers of yellow - grey rock comprise the Toroweap Layer, which holds significant fossil records from this ancient sea.

The Kaibab Sea was teeming with life; so much so that remains of its inhabitants piled up and formed a hard limestone called Kaibab Limestone. This durable limestone erodes slowly, typically into vertical cliffs and flat benches.

The Kaibab Limestone layer is lightly colored, 200 -300' thick and among the highest strata found in Sedona.

Tectonic activity over the millennia has exposed all of these layers to wind and water, which have sculpted them into the spires, buttes and mesas we see today.

Sedona: Red Rock - Secret Mountain Wilderness - Ecology

Sedona is located on the edge of the Mogollon Rim, a steep escarpment along the southwest edge of the Colorado Plateau. Elevations range from 4500' in deep red canyons to over 7000' on the wooded Mogollon Plateau.

Though Arizona is typically associated with the Sonoran Desert, Sedona's high elevations and latitude place it closer to the Colorado Desert biome. There are 7 ecosystems and subsystems found in the Red Rock - Secret Mountain Wilderness Area:

• Desert Grasslands


• Chaparral


• Riparian


• Arizona Cypress Woodlands


• Evergreen - Oak Woodlands


• Pinyon - Juniper Woodlands


• Ponderosa Pine - Fir Forest

Even subtle changes in elevation, sun exposure and the water table can have a profound affect on the variety and abundance of local vegetation:

THE FOUNDATION: CRYPTOBIOTIC SOIL

At the base of Sedona's iconic red rock monoliths is a living ground cover called cryptobiotic soil. Cryptobiotic soil is comprised of cyanobacteria and varying amounts of lichen, moss, green algae, micro fungi and bacteria.

Cyanobacteria is one of the oldest known life forms; it's thought these organisms were among the earth's first land colonizers, and integral in the formation and stabilization of the earth's early soils.

Cyanobacteria harvest the sun's energy through photosynthesis, producing oxygen that helped convert the earth's original carbon dioxide-dominated atmosphere into an oxygen-rich one capable of sustaining life.

When wet, Cyanobacteria moves through the soil and binds rock and soil particles, forming a fibrous mesh that stabilizes the surface.

Cyanobacteria is also critical to vascular plants, which are unable to utilize nitrogen as it occurs in the atmosphere. Cyanobacteria is able to convert atmospheric nitrogen to a form plants can use, a vital resource for native vegetation. Agave, cactus, yucca and desert grasses depend on these enriched soil beds.

DESERT GRASSLANDS

Desert grasslands occur in the most arid regions of Sedona from 3,000 - 5,000'. Blue grama, black grama, side-oat grama, creosote, yucca, whitethorn and prickly pear are primary constituents of these high desert grasslands.

Mesquite, palo verde and ocotillo can be found in pockets, but are more common in the lower elevations and latitudes of the Sonoran desert.

CHAPARRAL

The chaparral ecosystem frequently overlaps the higher range of desert grasslands. Chaparral is characterized by diminutive, woody brushes and shrubs such as manzanita, shrub live oak and mountain mahogany.

Plants of the chaparral are well-adapted to wildfire, and typically recover in full after these naturally occurring disturbances.

Many species are adapted to a particular fire cycle, which is based on the fire return interval, intensity, seasonality and other factors.

ARIZONA CYPRESS WOODLANDS

Arizona cypress woodlands occur at elevations matching the Hermit Shale formation, and at the higher, steeper range of the Schnebly Hill formation.

Arizona cypress is the only cypress native to the southwest, a medium sized tree that can reach 60' with a 15 - 30” diameter.

The AZ cypress is evergreen, with a dense, upright, cone- shaped crown and smooth reddish-brown bark that sometimes becomes fibrous with flat ridges. Leaves are scale-like and grayish-green, bluish-green or silver. Twigs and leaves can emit a fetid odor when crushed.

RIPARIAN

Riparian zones are defined and distinguished by the presence of water. Riparian woodlands are found adjacent to streams in the transitional zone between the stream and upland environment.

These lush corridors support a diverse collection of plants and trees, which in turn attract abundant wildlife. The region's wildlife - from butterflies to bears - depend on riparian corridors for survival.

Riparian corridors are known for deciduous (leafy) plants and trees that may not occur in any other local system. Cottonwood, willow, aspen, walnut, alder, sycamore and horsetail thrive in this moist environment.

Arizona Sycamore is one of the most conspicuous trees of this community, set apart by its constantly shedding white, brown and green bark.

Unlike other sycamores, the Arizona sycamore is only found along riparian corridors. The tree uses an amount of water, by weight, equal to the weight of its leaves every hour of the day.

EVERGREEN OAK + PINYON - JUNIPER WOODLANDS

Pinyon-Juniper woodlands are the most prevalent forest type in the middle and upper Mogollon Rim country. Juniper is a ubiquitous member of the cedar family found from desert grasslands to the Mogollon plateau. Oak woodlands intersperse and commingle with pinyon-juniper forests.

Pinyon nuts and oak acorns feed many birds and small mammals, and were essential to native American diets. The nutritional value of pinyon nuts is comparable to most commercial nuts.

PONDEROSA PINE - FIR FOREST

Ponderosa - Fir forests span the region's highest elevations. Ponderosa prefers dry, south-facing slopes in an open, park-like setting. Fir trees prefer cooler slopes and require wetter soil beds than ponderosa.

Ponderosa forests are naturally maintained by low-intensity fires every 5-15 years that keep populations and competition to a minimum. Mature ponderosa pine bark is resistant to such fires, while their cones rely on heat to open and release seeds.