SFBWR Buckshot or Cannonballs? Earthcache EarthCache
SFBWR Buckshot or Cannonballs? Earthcache
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
As an earthcache, there is no “box” or “container” to discover. Rather, with this cache, you discover something about the geology of the area. For more info, consult www.earthcache.org
This is one of a set of earthcaches that are part of the hiking trail system at Don Edwards San Francisco Bay National Wildlife Refuge. You may park at the visitor center to begin your journey. BE SURE that you have downloaded a copy of the trail map (visit link)
before beginning your hiking journey.
Logging Requirements:
Send the answers to #1-#4 to me through my geocaching profile.
1.List the name “GC2EV75 SFBWR Buckshot or Cannon Balls Earthcache” in the first line of your email. Also, list the number of people in your group.
2.What is the elevation at the listed cords? What MIGHT this elevation tell us about the source(s) of the weathering out process of the concretions?
3.Count the number of concretions in this rock face
4. Estimate the average SIZE of the largest concreation you see. NOTE: most concretions are dark brown "rusty" colored. These are in Serpentinite so are a DARK Blackish-green instead.
5. (pics are optional based on geocaching.com add'l logging req. guidelines, but having one sure does help me if your logging answers are otherwise "not quite right") Post a picture of yourself and/or your GPS with your log that shows the rock face behind you. If you're really NOT into pictures, you may measure the HEIGHT of the visible rock face that holds the concretions. DO NOT ESTIMATE if you choose this option.
I will only respond if you have incomplete logging requirements. Go ahead and log your cache
Refuge Information:
“Don Edwards San Francisco Bay National Wildlife Refuge, the first urban National Wildlife Refuge established in the United States, is dedicated to preserving and enhancing wildlife habitat, protecting migratory birds, protecting threatened and endangered species, and providing opportunities for wildlife-oriented recreation and nature study for the surrounding communities.”
A map of the hiking trails is available at: (visit link)
Geology:
A concretion is a “lump” of sedimentary rock that has become cement because minerals have filled the porous space between the sediment grains. Concretions tend to be spherical or orb shaped, though sometimes they are irregular in shape. The word 'concretion' is derived from the Latin con meaning 'together' and crescere meaning 'to grow'. Concretions “grow” in the sediment layers after the layer has already been formed. Basically, minerals in the rainwater or brought to the area through erosion seap into the sediment layers already in place. Because the cemented spheres are “harder” then the surrounding sediment, they often weather more slowly and thus become exposed in sedimentary rock faces as these softer rocks are eroded away. NOTE: Serpentinite has been metamorphised after sediment was laid down, so these concretions are "different then usual."
In this rock face you are looking at several concretions that are darker than the surrounding sediment. For the logging requirements, you will need to count how many concretions are exposed and estimate how large (in inches or centimeters) the concretions each are.
Resources:
Alt & Hyndman, Roadside Geology of Northern and Central California. Mountain Press Publishing. Missoula: Montana. 2000.
“Concretion” (visit link)
Don Edwards SF Bay Wildlife Refuge – (visit link)
Additional Hints
(No hints available.)
Treasures
You'll collect a digital Treasure from one of these collections when you find and log this geocache:
Loading Treasures