Monument Bluff: The Pinacate Volcanic Field EarthCache

This cache has been archived.

Geocaching HQ Admin: It has now been over 30 days since Geocaching HQ submitted the disabled log below and, unfortunately, the cache owner has not posted an Owner maintenance log and re-enabled this geocache. As a result, we are now archiving this cache page.

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Hidden : 1/1/2010
Difficulty:
5 out of 5
Terrain:
3 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

Possibly the southernmost volcanic structure in the continental U.S. that is recognizable as such to the layman.

Volcanic cones are among the simplest volcanic formations in the world. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and size of the fragments ejected during the eruption. Types typically differentiated are spatter cones, ash cones, tuff cones, and cinder cones.

Stratocone
Stratocones are large cylindrical structures built up around a main tubular volcanic vent by more than one eruption. Stratocones can form large mountains and possess a distinctive layering of lava flows and tephra.

Spatter cone
A spatter cone is formed of molten lava ejected from a vent somewhat like taffy. Expanding gases in the lava fountains tear the liquid rock into irregular gobs that fall back to earth, forming a heap around the vent. The still partly liquid rock splashes down and over the sides of the developing mound is called spatter. Because spatter is not fully solid when it lands, the individual deposits are very irregular in shape and weld together as they cool, and in this way particularly differ from cinder and ash. Spatter cones are typical of volcanoes with highly fluid magma, such as those found in the Hawaiian Islands. The spatter that builts up the cone can either be agglutinated or welded, the former meaning that the individual spatters pose one above each other with a lesser degree of welding occurring, while welded spatter is practically almost fluid when it lands and welds therefore easely.

Ash and tuff cones
An ash cone is composed of particles of silt to sand size. Explosive eruptions from a vent where the magma is interacting with groundwater or the sea (as in an eruption off the coast) produce steam and are called phreatic. The interaction between the magma, expanding steam, and volcanic gases results in the ejection of mostly small particles called ash. Fallen ash has the consistency of flour. The unconsolidated ash forms an ash cone which becomes a tuff cone or tuff ring once the ash consolidates. Flat-floored craters that scientists interpret have formed above diatremes as a result of a violent expansion of magmatic gas or steam; deep erosion of a maar presumably would expose a diatreme.

Cinder cone
A cinder cone is a volcanic cone built almost entirely of loose volcanic fragments called cinders (pumice, pyroclastics, or tephra). They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit.

Cinder cones rarely rise more than 300 to 750 m or so above their surroundings, and, being unconsolidated, tend to erode rapidly unless further eruptions occur. Cinder cones are numerous in western North America as well as throughout other volcanic terrains of the world. Parícutin, the Mexican cinder cone which was born in a cornfield on February 20, 1943, and Sunset Crater in Northern Arizona in the US Southwest are classic examples of cinder cones, as are the ancient volcanoes in New Mexico's Petroglyph National Monument.

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From the near-by El Camino del Diablo, this hill looks like any other ordinary hill. Once you reach the summit, you are immediately rewarded with a view of the inside of a fairly young volcanic crater. There are a few similar craters nearby to the north and east, and many more in the main section of the field to the south in Mexico. I noticed this crater while planning a trip over El Camino del Diablo, the floor of the crater has a rather interesting pattern.

Knowing that a traditional cache located on the Cabeza Prieta National Wildlife Refuge would be absolutely out of the question, I inquired at refuge headquarters in Ajo about the possibility of an educational cache that involved no physical container. Margot Bissell (Public Use Assistant) listened carefully to my intentions, and then went to ask her supervisor.
The answer was yes, but with two caveats:

1. Refuge personnel are REQUIRED to be accompanied by an armed Peace Officer whenever they enter the area south of the main road. There is no such requirement for visitors (civilians), but those choosing to venture there should keep a wary eye out for the possibility of encountering unfriendly visitors from the south.
2. Vehicular travel is not allowed beyond fifty (50) feet off the main traveled road.

There is a pull out near the smaller crater to the north...PLEASE PARK HERE! (see parking waypoint below) Any logs giving even the vaguest indication that they drove past the parking spot WILL BE DELETED, and the offender(s) WILL NOT be allowed to re-log. Any feedback from Refuge personnel citing increased vehicle tracks approaching the crater will result in archival of this cache.

LOGGING REQUIREMENTS

Send me (the cache owner) an EMail with the name and waypoint of this EarthCache as the subject.
Indicate the number of people in your party.
Include your answers to the following questions:

1. The rock along the top of the crater rim holds fairly clear evidence of what type of volcanic cone we have here. Based on your observation and interpretation of the information above what type of volcanic cone are you standing on?

2. Using whatever means you have at hand, estimate how high the middle monument along the rim is above the monument on the central mound in the floor of the crater. The base of each monument should be your measurement point.

In addition, your log MUST include a photo of your GPSr taken from the middle monument along the rim looking down at the monument on the central mound, and a similar picture taken from the monument on the central mound looking up towards the central monument on the rim of the crater. See the cache page images for qualifying examples.

OTHER REQUIREMENTS
A Range Pass is required to visit this remote area. They are given free of charge, but you will need to sign a 'hold harmless' waiver and invest a few minutes watching an informative video. Each adult needs their own pass, and if your group exceeds six vehicles special arrangements must be made well in advance of your visit. All vehicles must be 4WD.
For information on obtaining your pass:
* Luke Air Force Base, Gila Bend Auxiliary Field, Gila Bend, AZ 928-683-6200 or 928-683-6220
* Range Management Dept, Yuma Marine Corps Air Station, Yuma, AZ 928-269-7150
* Cabeza Preita National Wildlife Refuge, Ajo, AZ 520 -387-6483

Additional Hints (No hints available.)



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