Introduction to Geology Field Trip to Southern Papago Park, Curry Road

This sheet is meant to form the basis for a self-guided trip to the southern Papago Park area, just north of the Salt River. The field trip consists of a short hike across the small hills to the south of Curry Road, between Mill Ave. and Rural Road. The best place to park is in the small city park east of the hills, south of Curry Road. To get to the area from ASU, take Mill Avenue north across the Salt River and turn right on Curry, drive past the hills and look for the park on the right (south). Alternatively, take Rural north across the Salt River, turn left on Curry, and look for the park on the left, before the hills. From the park, hike to the west (toward Mill) across the hills.

The geology of this part of the Papago Park area is dominated by red-colored Cenozoic sedimentary rocks (about 20 to 25 m.y. old) that were faulted and tilted so that they now dip to the southwest. As a result of this dip, you can walk up through the sedimentary sequence, from oldest to youngest, just by walking westward across the small hills. As you walk to the west, you will encounter three main sedimentary units. The first and oldest unit is exposed in the rugged hills just to the west of the small park. This unit (located at point A on the map below) consists of shattered rocks that were deposited as a huge landslide right next to a big mountain that has been totally eroded away. Further west, at point B, is the second unit, which includes bedded sedimentary rocks deposited on top of the landslide by streams close to the front of the same mountain. The third and youngest unit, located still further west at location C, consists of finer grained clastic sedimentary rocks that were deposited on floodplains and in shallow lakes.

Your goal for this trip should be to see what you can observe about the three units on your own and try to convert your observations into a written description of each unit. You can use simple, nontechnical terms if you wish, or try to apply some of the new words you learned in class or lab. Characteristics you might want to observe include the following:

• the color of the unit as a whole (red, yellowish, gray; is it consistent or variable from place to place); is there desert varnish (a dark stain on the rocks) and, if so, is it on every surface or just some surfaces?
• the size, color, and roundness of clasts (pieces) in each unit (sand sized, small rounded cobbles, large angular boulders, etc.)
• the presence or absence of sedimentary layering (bedding), and the orientation of the bedding (how much and which way it dips)
• you might also try to identify what type of rocks the clasts were derived from (options include metamorphic rocks, volcanic rocks, granite, quartz veins, sedimentary rocks, etc.); this will tell you what the mountains were made of that were eroded away
• whether each unit forms rugged hills with little cliffs, steep slopes, or low, soil-covered hills (this tells you something about how resistant each unit is to weathering and erosion)
• fractures (joints and faults) in the rock
• how strongly cemented are these rocks compared to the sand and gravel deposits along the Salt River to the south? How much groundwater do you think these three units would hold, compared to the Salt River gravels?
  

You might try to think about what a simplified geologic cross section, drawn from east to west, would look like. First, sketch a profile of what the hills and valleys would look like when viewed from the south. Then show the three units, how they dip, and what you would expect to find in the subsurface beneath any place along your hike.

Finally, try to envision how the landscape looked when each of the three units was deposited. Try to envision how the landscape changed from unit 1 to unit 2 to unit 3 and what processes might have caused the change.

Be sure to click here to get the map too! You will need it!