Thursday, March 08, 2018

Spectacular Red Rock Cliffs near Flagstaff - Not Sedona!

Just outside of Flagstaff lies an unknown landscape - forgotten, wild, and surreal. The colors and textures are electric. My friend Scott Thybony took myself and three others out here on a blue-bird winters day in February. We live for this kind of exploration and were not disappointed.

The approach and the openness of a wild land.

Resembling a Navajo hogan, this rocky outcrop serves as a guidepost to the natural wonders of the Adeei Ecchi Cliffs. These strata belong to the eolian (wind-blown) Jurassic Wingate Sandstone (about 205 Ma). Just about 10 miles from here, the unit grades into the Moenave Formation, a fluvial (river) deposit. A reconstruction of the Early Jurassic landscape as documented by these changing lithologies, reveals a desert dune environments encroaching on an arid floodplain. The modern Persian Gulf is a great analogy.

First stop, a trackway site with over 400 dinosaur footprints.

Some are very well preserved with clearly delineated claw marks.

Moving toward the cliffs.

A preview of the strange erosional forms here.

Normally, wind has very little power in eroding and shaping landforms in the southwest. It does often transport grains away that are already dislodged. But the wind probably has little eroding power. The relatively weak cementation here allows for the likely sculpting by the wind.

Especially along weaker cemented horizons like the thin pedestal seem here.

Remarkable, isn't it.

Note the obvious cross-bedding highlighted by alternating layers of oxidized (red) and reduced (green to white) horizons along specific beds.

Looking out toward Gray Mountain to the west and the Grand Canyon area. Wide-eyed boys enjoying wide-ranging views,

An old Navajo hogan in ruins. The hogan is constructed of gray limestone beds from within the Wingate Sandstone. I had never before seen limestone beds from the Wingate. They are quite common in the overlying Navajo Sandstone and represent oasis' deposits during the Jurassic when the water table was high. If algae is present in the oasis ponds, calcium will be secreted and deposited. as limestone

A wonderland of seemingly jumbled rocks. But most of these have not moved and have merely weathered in place

During uplift, a consistent joint pattern is imprinted in the rock mass and erosion can attack these vertical lines of weakness to ultimately create ghost-like forms. Full moon night hike anyone?

Differential weathering - the well-cemented horizons protrude outwards, the weaker cemented horizons are indented. These conditions were imprinted while the rocks were still buried but upon being exposed, the forms take shape.

Cross-section of a dune. Note the darker wedges of sand coming in from the upper right. These are sand flow toes - formed when the crest of dune becomes oversteepened in a windstorm and then cascades down the leeward side. The direction of dip documents the direction of dune migration and wind direction. Sorry YEC's. These features are ubiquitous in arid dune environments today and the rocks were not formed in a world-wide flood from the Superstition Period. No offense meant - just sayin'.

One has to imagine that these forms are constantly changing - well, at least with respect to deep time. Something like this might change drastically in only 1,000 years. Or not.

Underlying the Wingate Sandstone is the Chinle Formation, soft gray mudstone that gives rise to the famous Painted Desert landscape. Here, Wingate Sandstone boulders have come to rest in equi-distant positions along the base of the small cliff. It reminded me of spokes in a wheel. Thanks Scott for a great day of exploration on our own two feet!

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