TO LOG THIS EARTHCACHE INCLUDE:
1. The name of this EarthCache on the first line of your email.
2. The number of people in your group.
3. Estimate or measurement of: 1) the horizontal orientation (strike) of the vein feature (number of degrees between 0 and 360); and 2) the vertical orientation (dip) of the vein feature (number of degrees between 0 (horizontal) and 90 (vertical), including the dip direction).
4. Which Big Ideas (1-9) are connected (list)?
5. Which GeoPrinciples (1-7) are relevant (list)?
6. Include a photo or 2 if you're so inclined (optional).
Note: In order to manage email volume, you may assume your responses are accurate if you do not get an email after logging this EarthCache. If a response is grossly inaccurate, you will not receive credit for the cache.
===============================================================================
RED HILLS GEOLOGY
The Red Hills is maintained by the United States Bureau of Land Management, or BLM (please follow the rules and regulations posted on their entry signs) and is an Area of Critical Environmental Concern (ACEC). The reason for the concern centers around the Red Hills’ unique geology, which creates the conditions that support many rare and sensitive plant and animal species, some of which live nowhere else.
The Red Hills is located within the Western Sierra Nevada Metamorphic Belt, in the Foothills terrane, and is sometimes referred to as the Tuolumne Ultramafic complex. It is bounded by fault strands of the Bear Mountains Fault Zone (BMFZ), which is a northwestward trending thrust fault system that dips steeply eastward. Rocks along the east side of the fault have been thrust up and over rocks to the west, displaying as much as 10,000 feet of vertical displacement. It is possible that the BMFZ once penetrated down to the mantle.
The Red Hills likely formed through the process of “protrusion". During protrusion, dunite (a rock rich in dark green olivine with minor chromite that forms at the top of the mantle/base of the crust) metamorphoses into the rock serpentinite, by taking on water at depth. It then swells, increasing the rock’s volume and thus lowering its density. The lowering of the rock’s density allows it to move upward, as a solid. This likely occurred along the BMFZ, bringing this rock from the earth’s mantle to the surface. The Red Hills’ dunite intruded into andesite pillow lava breccias and flows of the Peñon Blanco volcanic formation and was serpentinized to antigorite magnesite-magnetite. The reddish color of the soil results from oxidation, or “rusting”, of the iron and magnesium-bearing serpentine group minerals and the olivine in the dunite. In 1965, serpentinite was designated as the state rock of California. This is one of the largest serpentine bodies in the Sierra Nevada.
As you walk along the trail toward the EarthCache site, you will see weathered dunite and serpentinite on the way (the BLM has placed interpretive signs to help understand the natural history here). Once you have arrived at the GPS location for the EarthCache, and found the rock outcrop, you will see remnants of a magnesite ore vein system in the pit dug out by prospectors (see Figure 1). Magnesite is a magnesium carbonate (MgCO3), an ore of magnesium, and is used for pyrotechnics, flares, photographic lens coatings, flash bulbs, and more. It is also alloyed with aluminum to make cameras, horseshoes, baseball catcher's masks, snowshoes, and other items.
Figure 1: View of a pit prospected for magnesite ore. Measurement of the vein orientation should safely be made without entering the pit.
For this EarthCache, you will estimate or measure the 3D geometric orientation of the tombstone rock features. Geologists measure the attitude – called strike and dip – of geologic features in order to try to infer what stresses have occurred to the rocks or what happens to them underground in order to find more. This is a significant skill in mineral and oil exploration when trying to locate important resources such as minerals, metals, or hydrocarbons or other fossil fuels (oil, natural gas, coal, etc.) trapped beneath the earth’s surface. The orientation of the fractures in rock can also be important to understand how water (and other fluids) travel through rock. The Royal Mountain King Mine, an abandoned open pit gold mine, just north of Copperopolis, has had issues with arsenic-rich waters potentially leaving the mine site. The state of California was concerned the water could be contaminating groundwater wells downstream. These wells tap into water that migrates through fractures in the rock. Knowing the pathway of travel by understanding the fracture orientations is something geologists are trained to assess. The diagrams below (see Figures 2 & 3) can help you to assess the horizontal and vertical orientation of the rock features. Once you have located the tombstone rocks, record the 2 estimates.
Figure 2: Strike (horizontal direction of the rock feature) and Dip (vertical direction of the feature). The value for the strike of the layers in this diagram is east-west, which is 90 degrees. North is always 0 (or 360) degrees, while east = 90 degrees, south = 180 degrees; and west = 270 degrees. The approximate dip of the layers in this diagram = 45 degrees toward the north.
Figure 3: Using the right hand rule: 1. Place your right hand on the surface (if the feature you are interested in is visible). 2. Rotate your hand so that your four fingers point downward, toward the dip direction. 3. Finally, extend your thumb on the same plane. The direction which your thumb is pointing to is the direction of the strike. The direction of your fingers is the direction of the dip.
Geoscientists have to be skilled in several different areas. They need to be somewhat proficient in: math, physics, chemistry, biology, surveying, geospatial technologies (GPS, GIS, remote sensing, and webmapping), lab technologies (microscopes, spectrometers, etc.), computer use, and more. Career opportunities in the earth sciences include: geologist, hydrologist, mapping/surveying and geospatial technologist, watershed analyst, mineralogist/mining engineer, petroleum geologist, environmental scientist, natural resources scientist, and more. If you are interested in learning more, take a course at your local community college to get started.
==============================================================================
EARTH SCIENCE BIG IDEAS
The Earth Science education community put together 9 “Big Ideas” for the Earth Science Literacy Initiative (ESLI), shown below. Their purpose was to highlight the main concepts and ideas a person should understand to be literate in the earth sciences:
An Earth-science-literate person:
• understands the fundamental concepts of Earth’s many systems
• knows how to find and assess scientifically credible information about Earth
• communicates about Earth science in a meaningful way
• is able to make informed and responsible decisions regarding Earth and its resources
Which of these Big Ideas below do you think are most relevant to this EarthCache?
Earth Science Literacy Project:
1. Big Idea 1: Earth scientists use repeatable observations and testable ideas to understand and explain our planet.
2. Big Idea 2: Earth is 4.6 billion years old.
3. Big Idea 3: Earth is a complex system of interacting rock, water, air, and life.
4. Big Idea 4: Earth is continuously changing.
5. Big Idea 5: Earth is the water planet.
6. Big Idea 6: Life evolves on a dynamic Earth and continuously modifies Earth.
7. Big Idea 7: Humans depend on Earth for resources.
8. Big Idea 8: Natural Hazards pose risks to humans.
9. Big Idea 9: Humans significantly alter the Earth.
For more details see: Earth Science Literacy Initiative
===============================================================================
GEOPRINCIPLES
There are several fundamental principles, developed over time, that guide geological reasoning and critical thinking, listed below. Read each short description, then use your best judgement to determine which principle, or principles, best relate to this EarthCache.
7 Principles in Geology:
1. Superposition – the oldest strata are at the bottom of the sequence
2. Original Horizontality - layers of sediment are originally deposited horizontally
3. Lateral Continuity - layers of sediment initially extend laterally in all directions
4. Faunal Succession - fossils succeed each other vertically in a specific, reliable order that can be identified over wide horizontal distances
5. Law of Intrusive Relationships - the geologic feature which cuts another is the younger of the two features
6. Uniformitarianism - the assumption that the same natural laws and processes that operate in the universe now have always operated in the universe in the past and apply everywhere in the universe
7. Catastrophism - the theory that the Earth has been affected in the past by sudden, short-lived, violent events, possibly worldwide in scope
===============================================================================
LOGISTICS AND SAFETY
This site can be reached via the Serpentine Loop Road in the Red Hills ACEC. The EarthCache is located along the Interpretive Trail constructed by the BLM. To reach the trail there are 3 stream crossings that must be navigated. Water flows in the streams during the winter, and sometimes, spring seasons. A high clearance vehicle is recommended in order to drive to the parking area. The area can also be accessed by parking at Red Hills Road, then hiking up the road on foot and crossing the streams where there are boulders to help stay dry. The area is very hot and dry in the summer time and the best time of year to visit may be during spring when the wildflowers are in bloom.
Visitors to this site should plan ahead and prepare by:
• Knowing the regulations and special concerns for the area you are planning to visit (obeying laws that prohibit collection or destruction of artifacts);
• Carrying a map and a GPS unit and/or compass;• Staying on existing roads and trails;• Staying away from any/all mine shafts and adits;
• Planning for extreme weather, hazards, and emergencies;
• Being aware that cell phones DO NOT usually work in the rural areas away from the major highways;
• Leaving your travel plans with a responsible party, including the date and time of your return;
• Being aware of any natural hazards associated with the region (e.g. poison oak, rattlesnakes, mosquitoes, cliffs/steep slopes, etc., etc);
• Carrying a full-size spare tire, extra food, water, and warm clothing;
• Following the “Tread Lightly" and "Leave No Trace” philosophy.
===============================================================================
TO LOG THIS EARTHCACHE INCLUDE:
1. The name of this EarthCache on the first line of your email.
2. The number of people in your group.
3. Estimate or measurement of: 1) the horizontal orientation (strike) of the vein feature (number of degrees between 0 and 360); and 2) the vertical orientation (dip) of the vein feature (number of degrees between 0 (horizontal) and 90 (vertical), including the dip direction).
4. Which Big Ideas (1-9) are connected (list)?
5. Which GeoPrinciples (1-7) are relevant (list)?
6. Include a photo or 2 if you're so inclined (optional).
Note: In order to manage email volume, you may assume your responses are accurate if you do not get an email after logging this EarthCache. If a response is grossly inaccurate, you will not receive credit for the cache.
===============================================================================
Note: For a brief summary of the geologic history of the Central Sierra, see this EarthCache:
Dragoon Gulch EarthCache
===============================================================================
REFERENCES
1. Busby, Cathy J., Andrews, G.D.M., Koerner, A.K., Brown, S.R., Melosh, B.L., and Hagan, J.C., “Progressive derangement of ancient (Mesozoic) east-west Nevadaplano paleochannels into modern (Miocene–Holocene) north-northwest trends in the Walker Lane Belt, central Sierra Nevada”, Geosphere 12, p. 135-175, 2016, http://www.geosphere.gsapubs.org.
2. Busby, Cathy J., Koerner, Alice, Hagan, Jeanette, and Andrews, Graham, 2012, “Sierra Crest graben: a Miocene Walker Lane Pull-apart in the Ancestral Cascades Arc at Sonora Pass”, in, N. Hughes and Garry Hayes (eds), “Geological Excursions, Sonora Pass Region of the Sierra Nevada”, Far Western Section, National Association of Geoscience Teachers field guide, p. 8-36.
3. "California State Rock", http://www.netstate.com/states/symb/rocks/ca_rock.htm, page last updated: April 21, 2015.
4. Earth Science Literacy Initiative (ESLI), 2010, http://www.earthscienceliteracy.org/.
5. Konigsmark, Ted, 2003, “Geologic Trips: Sierra Nevada”, GeoPress.
6. Landefeld, Leslie, and Snow, Geoffrey, "Guide to Yosemite and the Mother Lode gold belt : Geology, Tectonics, and the Evolution of Hydrothermal Fluids in the Sierra Nevada of California : with articles on Operating Mines in the Mother Lode, Land Use & Permitting History, and Natural History of the Sierra Nevada” : June 6 to 9, 1990, Ventura, Calif. : Pacific Section, American Association of Petroleum Geologists, 1990.
5. Portland State University, “Glaciers of California”, last updated 08-04-2011, http://glaciers.research.pdx.edu/glaciers-california.
6. Putnam, Roger, (pers. comm.), May 2017, Professor of Earth Science, 11600 Columbia College Drive, Sonora, CA, 95370.
7. Schweickert, Richard, 2006, “Accretionary Tectonics of the Southern Part of the Western Sierra Nevada Metamorphic Belt” (modified from a 1999 guidebook article by Schweickert, Girty, and Hanson), in J. Tolhurst (ed), “Geology of the Central Sierra”, National Association of Geoscience Teachers Far Western Section Fall Conference field guide, p. 55-95.
8. U.S. Bureau of Land Management, "Red Hills Home Page", http://www.blm.gov/ca/st/en/fo/folsom/redhillshomepg1.html, last updated on 06/22/2010.
===============================================================================