Re: Questions from a YEC convert

Arthur V. Chadwick (
Sun, 30 Nov 1997 13:31:20 -0800

At 08:50 AM 11/30/97 -0600, Glenn wrote:
>Fascinating example. Since you have seen this and I haven't, let me ask a
>few questions.
>How do you distinguish the time of the deformation. In other words could
>this be a deformed block of Redwall which subsequently slid down the
>mountain. The deformation having taken place long before the slide.
The deformation conforms to the underlying irregularities of the Tonto
surface upon which it came to rest.

>How do you rule out a slope failure which caused brecciation at the time of
>the fall and then re-cementation.

It is a very thin slab. To become recemented in place it would have had to
slide as a unit with enough integrity to prevent fragmentation. It has
come down several hundred feet of topographical relief, presumably over a
ramp which no longer exists. If the slab was fully lithified and it became
brecciated during movement, its present level of integrity could not have
been maintained. I will try to get some photos up where you can see them.
>I guess I need clarification on whether the deformation you speak of is
>WITHIN the various blocks of Redwall or BETWEEN the fragments of the Redwall.

The whole slab is deformed by the irregularities of the surface on which it

>Concerning the slumps into the canyon: Slumps occur along any steep slope.
>If an entire section of paleozoic rock slumped into the canyon, I wouldn't
>find that surprising. What I would find surprising is internal deformation
>of the block which slid--deformation not caused by fracturing but by soft
>sediment flow. It is the internal morphology of the blocks which is
>important and I can't get that info from what you wrote.

What is *surprising* about the Surprise Valley slump is that it is huge and
does not appear to be associated with any known faults (except it is of
course itself fault bounded) and is a Toreva-type slump (base outward
rotation). This type of slump occurs most readily in unconsolidated or
partially consolidated materials, and the present condition of the canyon
walls certainly does not encourage this kind of development.

>Can you refer me to any articles where I can read about this?

There aren't any on this particular locality. However it is reasonably
easy to access from the South Kaibab Trail, and anyone wishing to do so may
easily get there.