WHITE TANK MOUNTAINS REGIONAL PARK EXTRA CREDIT PAGE
The above picture is a view from Waterfall Canyon trail Waterfall Canyon is in the shadows just to the left of center.
LOCATION: The White Tank Mountains Regional Park is located in western Maricopa county. It is most easily accessed by taking Olive Ave west. Olive Ave continues into the park. This is a day use facility and you are required to pay a fee upon entry. Park hours are from sunrise to sunset. As of February 2003 the entry fee is $5.00 per vehicle and $1.00 to bike into the park.
PROCEDURE: As you drive through the park, the road will take you past many picnic areas and trail heads. Park at the Waterfall Canyon trail head and parking area. This is a very popular trail and is moderately maintained.
NOTE: One group of students had their car broken into and a purse, textbooks and stereo were stolen. Do not leave valuables in the car. If you have no other choice be sure they are at least out of sight.
GENERAL GEOLOGY: The White Tank Mountains are named for the "white tanks" found within the park. Tanks are a southwestern term for depressions that accumulate water after the infrequent rains in the desert. Here, the tanks are along stream drainages. As you travel through the park you will notice that most of the rocks are dark in color. But as you pass by streams the color of the rocks is a very light gray. The dark color of the rocks on the hills is a surface coating called desert varnish and is an accumulation of iron and magnesium oxides that forms over long periods of time. The rocks that make up the mountains are granites and high grade metamorphic rocks like schist and gneiss which have a "granitic" composition (quartz, feldspar and muscovite mica).
METAMORPHIC CORE COMPLEX: Specifically, the White Tank Mountains are an example of a metamorphic core complex. Proterozoic aged metamorphic rocks (about 1.3 billion years old) were intruded and deformed by Late Cretaceous to Early Tertiary igneous plutons during the Laramide Orogeny (about 60 million years ago). These rocks were brought to the surface by mid Tertiary faulting (20-30 million years ago).
As you drive into the park, just past the Visitor Center, you will climb a small hill. On both sides of the hill are interesting outcrops.
On the right side (east) of the road notice the accumulation of sediment and the crude soil zone as shown in this image:
The image below shows the old erosional surface as a red line. If the sediments on top of this line were lithified to a sedimentary rock, which sedimentary rock would it be AND what type of unconformity would be formed? The rocks below the line are schists and gneisses.
| Rock Type - |
| Type of Unconformity - |
Note also that there has been displacement along another line (red line).
Use arrows on this photograph to show the relative movement along the fault.
On the west side (left side as you drive in) of the road you can see some interesting folding in the high grade metamorphic rocks.
This view
of the roadcut shows a mixture of quartz veins in the high grade metamorphic
rocks.
The above picture is a close up of the outcrop showing a highly folded and fracture quartz vein. What must have been the conditions millions of years ago for this brittle rock to behave in such a plastic manner?
Also, at this same outcrop, is a highly weathered portion of the rock. It is so weathered that it easily breaks in the hand. This highly weathered zone is along a fault. The fracturing of the rock provided an avenue for water to percolate. The most vulnerable minerals (most commonly feldspars and micas) succumbed to the acids in the water.
What naturally occurring acid is was responsible for this chemical weathering process?
Acid: _____________________________________
THE REST OF THE QUESTIONS ARE FOR THE WATERFALL CANYON TRAIL.
TRAIL GUIDE: This trail guide is referenced to the many memorial benches that have been constructed along this popular trail as well as other obvious landmarks. Mileage is from the beginning of the trail and is straight line distance - obtained by using GPS. (Be sure to protect your property before you leave your vehicle.)
STOP 1: (.23 miles from trail head) Concrete wash crossing and the Sean Henley Bench.
What is the mineral composition of the sand in the wash?
Describe (or sketch) the angularity of two of the larger grains of sand from the wash.
STOP 2 (.33 miles) Rippelmeyer Bench This rock is along the trail:
Is this a natural feature of the rock or not. Explain your answer.
STOP 3 (.36 miles) Petroglyphs This is a large meeting area with many petroglyphs on the surrounding rocks.
What are the petroglyphs, how were they made and about how old are they?
What type of NATURAL weathering is taking place on the surface of the rocks in this area? (Remember that weathering is the breaking down of the exposed rock by mechanical or chemical methods.)
On the south side of the trail, 30 - 40 (at 0.39 miles) yards past the ramadas, is a large boulder.
What type of rock is it? ________________________
What minerals does it contain? __________________________________
The cracks developing along its surface are an example of exfoliation. How does this develop?
STOP 4: (.42 miles) This is a boulder along the south side of the trail
This deposit of crystals was along a vein. The rock split along this vein so that the crystals are exposed on the surface of the rock. Looking at the shape and the color and how the mineral breaks, what mineral is it?
Mineral: _________________________________
STOP 5: (.47 miles) Lee and Collins Benches From this spot notice the color of the rocks high on the north hillsides and the color of the rocks in the wash. Describe the color of each and explain the difference.
| HILLSIDE | WASH |
Are they the same rock type? _________________________________
Notice the sediments on the bank on the south side of the wash.
Describe the degree of sorting displayed in this exposure. Comment on the angularity of the sedimentary grains and what was the mechanism of transport and deposition?
Also at (.47 miles): Looking at the rocks in the wash, how can you determine which boulders (roughly the same size) were transported the greater distance? (There are two very big boulders in the wash that illustrate this question very nicely>)
Just a bit further up the trail (100 feet or so) is a telltale sign of faulting. It is called slickensides. It is produced when rock (under pressure) break, and slip past one another. It produces a thin layer of finely pulverized rock that feels smooth as you move you hand along the direction of movement of the rocks and rough in the other direction.
These pictures are the view of the slickensides along the outcrop on the north side of the trail. The photo was taken just a few feet past the exposure. The right picture is a closer view. (If you have a GPS the coordinates are: 33o 35.134N and 112o30.858W) (It is at 0.48 miles from the trailhead.)
STOP 6: (.54 miles) Just off the trail on the right is a boulder with petroglyphs.
Upon closer inspection you will notice that these petroglyphs are much fainter that the other petroglyphs in the area. What natural process could account for the difference in the amount of desert varnish on this rock versus the other petroglyphs ?
REFERENCE (.71 miles) - Water Tank (bullet riddled)
STOP 7: (.73 miles) (Trail forks just past Olson bench (about 14 yards) - take the left fork.) From this spot in the trail, walk about 50 feet toward the creek (see photo). This will provide a view of the wash that contains many granitic boulders. From this portion of the trail, as you look to the canyon walls to the south, you will see a fine example of desert tapestry - an obvious dark stain on the canyon walls.
Here are pictures of this detour from the main trail:
Origin of Desert Tapestry: Speculate on its formation, keeping in mind the drainage of the area.
BOULDER INVESTIGATION: Among the boulders you will notice many signs of water erosion. Study the upstream side of the boulders and compare their surfaces with the downstream side of the boulders.
Observations:
What evidence among the boulders in the wash can you find that indicates that the larger boulders have not moved very much? (Other that the fact that they are more angular.) (HINT: Look closely at the area where the water flows.) - From here return to the main trail.
REFERENCE: (.76 miles) Trail forks, keep to the right and under trees. Look for the rock and mortar steps. (The trail is a bit rougher from here to the end.)
STOP 8: (.78 miles) This is the last stop and is just below the falls - where the trail ends at a pool (usually containing water). There are very good examples of channel cutting and water worn rocks along the wash here.
33o 35.051' N and 112o 31.158' W
In this image (just below the end of the trail) 4 rocks have been labeled.
Which of these boulders has spent the least amount of time in the channel - A,
B, C or D ? Explain your answer.
Here is another portion of the stream channel near the end of the trail. Notice the boulder on which sits the Brunton Compass. This boulder has been colored violet in the right picture. Speculate as to the unusual erosion of this boulder. (The dark stain to the right of the compass is a trickle of water flowing over the boulder.)
The picture below shows a quartz vein that has been offset in a number of places (the quartz vein has been shaded green). In addition to this evidence of displacement, there are small parallel grooves and polished surfaces along the walls. These are more "slickensides". The smaller picture can be enlarged for a closer look.
The left picture is the view at the end of the trail looking up to what would be a waterfall in wetter weather. The middle picture shows the waterfall in January of 2005. The right picture is water flowing into the lower pond below the waterfall.
Based on these observations, why is Waterfall Canyon located in this particular spot?
THIS PROJECT IS WORTH A MAXIMUM OF 15 POINTS OF EXTRA CREDIT.