Conor Watkins And J. David Rogers
Colorado Plateau Research
Toreva, AZ Landsliding

In 1937, Parry Reiche recognized the Toreva block as a unique style of landslippage in a Journal of Geology article titled "The Toreva-block, a distinctive landslide type."  The name emanated from his type locality in the vicinity of Toreva, a small town in the Hopi Indian Reservation near Black Mesa in northern Arizona.  Toreva is located on the southern end of Second Mesa about 100 miles due north of Winslow, AZ.

He subsequently noted the occurance of these slides throughout the Colorado Plateau and pointed out their presence along the Vermilion Cliffs, in the Grand Canyon, and other areas, mostly escarpments.  Toreva blocks have also been termed rotational landslides, earth and rock slumps and slump-flow landslides.  This type of slide most often occurs where weak shales are overlain by more competent beds, such as sandstone and limestone .  The weaker rock typically shears along a lystric failure surface, which Leo Rendulic first recognized to be log spiral shaped in 1935. As the sliding block translates it rotates backward along the log spiral shaped rupture, casuing the block to rotate backward towards their scarps.  The Cretaceous Mancos Shale is responsible for the failures observed near Toreva.

Original Parry Reiche article The Toreva Block, a distinctive landslide type
-From Journal of Geology Vol 45, No 5, 1937

Vicinity map of the area surrounding Toreva on Second Mesa on the Hopi and Navajo Reservations in northeastern Arizona.  We have also recognized similar landsliding along First and Third Mesas.

This topographic map (click map for better image) shows the incised escarpment surrounding the southern end of Second Mesa.

This is Reiche's sketch showing a plan view and cross section line through the Toreva blocks bordering Second Mesa.  Reiche was working for the U.S. Soil Conservation Service at the time he authored the original article.

This arial view looking north at the southern tip of Second Mesa shows the front of several Toreva blocks that have failed at the type locality.  Note that the mesa is capped with the lighter colored Mesaverde Sandstone Formation.

An aerial oblique view looking down the strike of several Toreva blocks shows repeating tilted strata of of both the Mancos and Mesaverde Formation.

Closer view of the Toreva Blocks at the southern end of Second Mesa

Geologic cross section along the southern tip of second mesa showing repeating strata and inferred failure surfaces (from Reiche, 1937).  A-B is denoted in Reiche's shetch above.  Note failure of slides against the northerly regional dip.

The Toreva Blocks at Second Mesa as viewed from above and behind.  One can see the repeating strata of the Mancos and Mesaverde Formations.

Wide angle view of the southern end of Second Mesa showing a series of retrogressive slumps near Toreva, AZ

This combination of two pictures clearly shows the landsliding and repeating tilted strata near Toreva, AZ

This closeup shot of the Toreva Blocks shows several of the slumps at the southern end of Second Mesa.  Notice the mobile home trailer on the slide for scale.

Sketch of a typical Toreva Block with a log spiral shaped failure surface in Surprise Valley in the Grand Canyon.   Note the back-rotated beds.  Toreva Blocks along the Vermilion Cliffs exhibit similar profiles, but within different formations.  The slides at Toreva floor in Mancos Shale while those in the Vermilion Cliffs occur mostly in the Petrified Forest Member of the Chinle Formation.  This sketch is taken from "Geology of The Grand Canyon, 3rd Edition", 1979.

This portion of nearby First Mesa on the Hopi Reservation shows a mesa in its final stages of erosion.  One may notice the regional joints, which are open near the left of this image.

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E-mail Dr. J David Rogers at
or Conor Watkins at