GC5ZKC9 CO - RRPT - Missionary Ridge Rockfall
Type: Earth | Size: Other | Difficulty: | Terrain:
By: PathfinderMark @ | Hide Date: 07/18/2015 | Status: Available
Country: United States | State: Colorado
Coordinates: N37° 18.705 W107° 51.210 | Last updated: 08/30/2019 | Fav points: 0
       

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This earthcache is part of a series of earthcaches available between Durango and Silverton, primarily accessible via the Railroad though also available via car.  

Suggested tools:  Notepad, camera (to help record information to help you complete ALRs)

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Missionary Ridge is on the east side of the Animas Valley.  It contains and displays an impressive sequence of Permian through Cretaceous sedimentary rocks.  

Logging Requirements: (My preference is that you send the answers through the new "Messenger" feature)
1.  Where on the ridge is the landslide located
A.  Southern edge near the top (Dakota through Morrison)
B.  Central portion mid-way down slope (Morrison through Dolores formation)
C.  North portion near the top (Dakota through Morrison)
D.  North portion near mid-way down slope (Morrison through Entrada)

2.  Why has the rockfall debris area become such a large area on the ridge (geologically)?  Based on your answer, would you consider the formation "competent" or "incompetent"? (see definitions below)

3.  What percentage of the ridge (vertically) has become involved in the rockfall at the time of your visit? 

 

Geologic Formation Descriptions - from bottom to top:

• Cutler and Dolores Formations- two distinct shades of red - because of the oxidized iron (hematite) shows evidence of arid continental conditions when this was part of ancient supercontinent Pangaea.
• Entrada Sandstone - white - preserves a Jurassic field of sand dunes which were later inundated with shallow waters and streams (see next layer)
• Wanakah, Junction Creek Sandstone, and Morrison formations - gray - these three formations are indistinguishable from each other from across the valley.  The Morrison formation is composed of mudstones and thus they erode at a greater rate, causing them to be subject to erosion and undercutting  (and thus rockfalls).   These formations came about because of stream or shallow water sediment deposition.  
• Burro Canyon and Dakota Formations - these erosion-resistant layers cap the ridge.  They are the main reason that this ridge stands above the Animas Valley.

In 1998, a large block of the Dakota Sandstone fell and  broke apart, scouring away trees as it fell.  During subsequent spring seasons after heavy snow, the Morrison Formation mudstones became saturated an can 
flow downslope as mudflows and debris flows now that the snope is not protected by caprock and vegetation.  

Definitions:
Rockfalls - Rockfalls are an evidence of erosion.  They are more visible than some other versions of erosion because of the size/magnitude of the geologic features (boulders) involved.  Rockfalls are caused when  large quantities of rock fall freely from a cliff face.  "A rockfall is one or more fragments of rock that are detached by sliding, toppling, or falling.  The rockfall then falls along a vertical or sub-vertical cliff, proceedsd own slope by bouncin and flying along ballistic trajectories or by rolling on talus or debris slopes." (Matthews, "Geology of the Silverton-Durango Train Route")  Sometimes, rockfalls fall, bounce, roll, or slide down a slope and form a tallus slope at the bottom of the rockfall.

talus/scree - simply, a pile rocks of large to small size that accumulate at the bottom of an incompetent cliff/slope as a result of rockfalls.

competent cliff - a cliff (formation) that contains well consoladated rock is stable and therefore not likely to be susceptible to rockfalls.  Mechanical erosion such as from roots or rain doesn't have a significant effect on this type of formation.

incompetent cliff - a cliff (formation) that contains largely unconsoladated rock and therefore is susceptible to rockfalls.  Mechanical erosion shuch as from roots or rain has a significant effect on this type of soft-rock formation.

07/03/2019 By okls1596
Thanks! Hortcacher and I enjoyed your earthcache. We hear and witness our local environmental events in Oklahoma such as thunderstorms, flooding, tornadoes, etc. I just can’t image witnessing a rock slide of this size.

07/03/2019 By hortcacher
OKLS1596 and I visited this earthcache after we visited Chimney Rock National Monument today. The slide area was immediately noticeable as we drove towards it. We had difficulties finding a place to park while we organized our thoughts, but we were able to quickly collect our information and go on our way. The answers to the questions have been sent through the message feature of the Geocaching app. Thanks for creating and maintaining this earthcache!

07/02/2019 By Paperballpark
#4753. I took a ride on the Durango and Silverton Railroad today, and was fortunate to be able to do this cache on the way. An interesting subject, and I've emailed my answers to the CO. TFTC!

06/03/2019 By LasCabrasDeMontanas
I sent you a message; but, it didn't seem to process correctly. I'll check on it tonight. TFTC

04/16/2019 By Benicha
Wow. Very interesting. Thanks for the lesson PathfinderMark. And this is still moving! yikes.

10/14/2018 By dover
Checked out Sunday on the way to Trimble. TFTC

10/13/2018 By BluePearl
How convenient to have this earthcache available today, Earthcache Day, so that we could find it the one day we are in Durango and get the souvenir! Thank you for creating this earthcache. It is interesting to see a recent geologic event, since usually we are talking tens of thousands of years. Answers will be on their way.

10/11/2018 By labpepl
The hardest part of this Earth cache was finding a place near the GZ to stop! A very interesting geologic phenomenum.

10/10/2018 By owlover
Geo road trip to the four corners to geocache with friends. Rain,sun and hail did not dim our spirits.

10/10/2018 By kayothree
Traveling in Durango and labpepl, Owlover and I love stopping for earthcaches. Thanks for creating the ec!

07/27/2018 By norbert28
Thanks for the earthcache! Found with mom - jasperdakota

07/27/2018 By jasperdakota
Thanks for the earthcache! Staying in Durango for a couple of days.

03/08/2018 By FLtravelers
We had no intention of coming this far north when we headed west for the winter. Somehow we "drifted" up here. Thankfully the roads were clear, but the snow made caching a bit of a challenge for this Florida couple. Great spot. TFTEC.

02/18/2018 By kapeka
Los Bastardos Finlandeses = LBF (J&T., laalaa and kapeka) in Tour. Today from Bloomfield to Green River . We had fun. Nice view.
Thanks for the earth cache.
Greetings from Finland.

02/18/2018 By J&T.
Team Los Bastardos Finlandeses on a Geocaching road trip in United States. Team consists of three names: kapeka, laalaa and ours. We used our stamp to log the caches or writed LBF to smaller logs. On two week trip we drove about 3000 miles through six states (California, Arizona, New Mexico, Colorado, Utah and Nevada) and made a quick visit behind border to Mexico, Los Algodones.

At Yuma, Arizona we had nice sunny weather when we were at the mega event. But later at Tucson and Phoenix area we got some rain and later at Utah temperature was 10F and it rained some inches of snow. That slowed us down little bit but we did found quite a bunch of caches on our trip. We found nice caches, had a fun trip and saw many beautiful places.

Today our journey continued from Bloomfield, New Mexico to Green River, Utah. The weather was nice but it was a bit cold. Still much warmer than -15F at home. Early in the morning we found some caches from Bloomfield area, before heading to Colorado. This was interesting Earthcache. Message sent to CO. Thanks for the cache and greetings from Finland!