Physical Geology Field Assignment

Part I

Igneous – Creek, Coalinga

The area I chose to collect many of my igneous rock samples was in the creek that runs through Coalinga. I was searching the creek in the section that runs under SR33 where the Indian burial grounds are. There hasn’t been running water in this creek for many years and there are many good rock samples from which to choose.

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My first igneous rock sample is very smooth and somewhat layered. It is brown in color and I was not able to determine what type of rock this is. It has a distinctive pattern on the back, however I can’t make it out because the rock was broken in half. Therefore, I am not sure if this pattern is from the rock being pressed against something hard for a long period of time or if it is some sort of fossil pattern.

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My second sample, I believe is Quartz. It is white with distinct layering. I found this sample in the area of Archer Mine in the Los Gatos Canyon. This area is known for quartz rocks and coal samples. Mineralization in this area are igneous rocks and sedimentary rocks, sandstone and shale.

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My third sample looks like it is obsidian. It is flat on one side and very black in color. It has a little white on the back. I also found this on the bottom of the creek bed in Coalinga by the indian buriel grounds.

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My fourth sample I believe is Red Jasper. It is entirely red in color with definite layers and markings. It is also flat on both sides. I found this rock in Jacalitos Creek just past Parkfield, CA. There are many small hills in this area and a creek bed where a nice little stream used to run.

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My fifth sample is Granite gabbro. It is black with layers of white running through it. It also has a crystallized look to it. This particular rock was a little tougher to get. I could barely see a little bit of it sticking out of the dirt. I had to dig it out of the dirt to really look at it.

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My sixth sample was also found in the creek bed by the Indian burial ground. After extensive research to try and identify this particular sample, the closest I could come to it is pegmatite. It is very colorful with gray, white and orange. It also has what looks like small gas bubbles or maybe some sort of fossilization.

Sedimentary – Atlas Asbestos Mine

The following sedimentary rocks I found next to and around the Atlas Asbestos Mine in the Los Gatos Creek area. This area has many hills, some trees, out buildings and the mine. This mine operated from 1963 to 1979 and it is an area known for its many sedimentary rock samples. They are all around the mine and the surrounding area. The mine, buildings , etc. covers 435 acres of land.

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My seventh sample I believe is clay. It is a deep red in color and relatively flat on both sides. I collected this while on the Parkfield-Coalinga Road on my way to Parkfield, CA. It was in an area that that is entirely hills, mountains and rock formations. It had been part of a bigger rock up on top of a hill and some of the bigger rock had broken into smaller pieces and looked like part of a landslide as I saw pieces of this same rock completely covering the hill all the way down the hill to the road.

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My eighth sample as with the others was found at the Atlas Asbestos Mine. This sample appears to be limestone. It is mostly black with many white lines running through it. It also looks like it has a few fossils in it.

Metamorphic – Coalinga Coal Mine, Los Gatos Canyon

The following samples were found at the Coalinga Coal Mine farther up in Los Gatos Canyon. This mine was in operation from 1962 – 1974 and covers 120 acres of land. While I was there looking for samples, I noticed that this area has an enormous amount of Metamorphic rocks along with sedimentary rocks.

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My ninth & tenth samples both look like slate. They are both quite similar. Both are dark red and layered. However, the sample on the right is flat on one side and is either fossilized or was pressed hard enough against something for a long period of time to make an imprint on this rock.

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My eleventh & twelfth samples look different from the previous two. The eleventh one is slate. It is orange with some black spots and layered. It has small spots of white in it also. The twelfth one is also slate but there are definitely two fossils in this one. One fossil looks like the face of a girl smiling. This rock is gray with a little white in it. These were also found by the Coalinga Coal Mine.

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My thirteenth & fourteenth samples are two completely different rocks. They both are metamorphic but #13 I think is schist. It is very coarse and medium brown in color. It also has a white line running through the middle that is almost perfectly straight. On the back it looks like it has a couple little caverns toward the top. Sample #14 is either quartzite or has quartzite in it. It is mostly white with a little bit of light gray. The entire rock doesn’t look like quartzite but there are some spots in the middle of the rock that definitely look like quartzite. This rock was found near the entrance of the Coalinga Coal Mine.

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My fifteenth sample was found in what is now known as Avenal, CA. I discovered that hundreds of years ago, this particular area of Avenal had been at one time a beach. This sample I believe is petrified wood from the shore of this ancient beach. I couldn’t find anything like this rock on the internet or in our textbook. Finally, I went to the R.C. Baker Museum here in Coalinga. They have many beautiful rocks on display and I found one very similar to this one that was petrified wood so that is why I think this is petrified wood. Also, it is rather delicate.

Physical Geology Field Assignment

Part II

Parkfield, CA

The small town of Parkfield, CA is approximately 30 miles from Coalinga. It is off Hwy. 198. After you turn on Parkfield-Coalinga Road you see nothing but hills, mountains and rock formations until you get to downtown Parkfield. There is also quite a variety of livestock. Parkfield has a population of 18. It is known as the earthquake capital of the world. I went there to take pictures of the fault and found so much beautiful scenery I hated to leave.

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After driving through the main part of town, we pass the fire station and the USGS trailer they use for an office. Then we come to the bridge. It is called the San Andreas Bend Bridge. This picture is of the sign you see on the bridge. San Andreas Fault Now Entering North American Plate.

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A Then we drove across the bridge to the other side and we found another sign that said, “San Andreas Fault Now Entering Pacific Plate”. This picture is of that sign.

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A This picture is of the San Andreas Bend Bridge from the “Pacific Plate” side of the fault line.

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This picture shows the land below the bridge which is the actual San Andreas Fault line that runs through the middle of Parkfield. The town is monitored by the USGS. As I said earlier, they have an actual trailer/office right next to the fire station. They have several monitoring units that are placed around Parkfield, however; we could not get pictures of these as they are set up on private ranches.

Fault – Parkfield, CA

After I took the previous pictures of the San Andreas Bend Bridge and the San Andreas fault line itself, we proceeded back to town heading home to Coalinga. We decided to stop at the USGS office. On the bulletin board, they mention that the Pacific Plate is moving constantly due to the daily earthquakes in Parkfield and that the bridge is also moving about 1 ½” per day.

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So we drive back to the San Andreas Bend Bridge to get a look at the movement of the fault line and the bridge. If you look toward the far end of the bridge and on the left bridge railing you can see a slight curve to the right. Right where that curve in the bridge begins is the center of the fault line. That is also where the Pacific Plate has been shifting a little bit every day. Lastly, that is why they call it the San Andreas Bend Bridge.

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This is my final picture regarding the San Andreas Fault that I located in Parkfield, CA. This picture is a picture of a map of California. It show the locations in California that have a high probability of having a large earthquake in the next 30 years.

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This picture is an example of mechanical weathering. It is a medium size rock that began its life on the ancient beach in the area we now call Avenal. It is part of a larger rock that was made when the ocean crashed on the sandy shore of the beach. This caused many precious rocks and seashells to be trapped in this section of sand that hardened into rock over the years. Look carefully at this view of the rock and you can see an entire face. You see (2) eyes, a nose and a mouth.

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This picture is a different side of the rock in the previous picture . However; if you look closely you can see a perfectly formed sea shell. It is not even chipped or broken. It is perfect.

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This is the third picture I have showing weathering. It is the same rock as the previous two slides only a different view of the rock. This view shows a fossil in the rock made of sand that looks very similar to a miniature skeleton. No matter what side of the rock I look at, I see fossils, sea shells and small rocks or pieces of rocks. It makes me wonder how many of these rocks, shells and fossils I would see if I broke this rock open and looked at the center of it. This rock is probably the most amazing rock that I have ever looked at.

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One example of mass wasting is a landslide or avalanche. I also discovered this example of mass wasting on the Parkfield-Coalinga Road on my way to Parkfield, CA. This picture shows this very large rock on top of a hill. This rock is black along the sides and the back of it and orange in the front of the rock. Directly below the rock is what looks like a pile of smaller rocks however; that is where the landslide began.

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In this picture you can see the rocks that slid down from the big rock in the previous slide and ended just a few feet away from the road. Also somewhere among these rocks in the side of the hill is a cave. However; we tried to see the entrance to the cave but it appeared to be covered by the rocks from the slide. This was on Parkfield-Coalinga Rd.

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Erosion is where rocks or other material is physically moved by water, wind or ice. There are different types of erosion. This picture is also from the Creek in Coalinga. It is at the higher end of the creek bed. In the background is the inside of the far wall of the creek. You can see definite holes where stream erosion has taken place. These holes are rather large so either large rocks or debris was the cause of the erosion or hundreds of smaller rocks coming through the stream at the same time.

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Farther down the creek I took this picture. This is also stream erosion on the inside of the same wall however; it looks quite different from the previous picture. Here you see rounded areas taken out of the wall almost like an extremely large hand reached out and grabbed a handful of the dirt and rocks that is consistent in the walls and bottoms of creek beds.

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This last picture is again at the creek. It is a different type of erosion. The top side of the creek has several large areas where you see this layered effect as in this picture. You can see gullies throughout where erosion has taken away the dirt and rocks that once make this area smooth and flat.

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This picture shows the creek from a different view. This is one end of the creek that is located near the Coalinga Regional Hospital. You can see quite a bit of plant life in this area of the creek but not in any other area of the creek for a number of miles. This particular picture shows the right tributary where water once ran through and into the main tributary of the creek farther down.

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This picture is in the same area of the creek as the previous picture however; this is the left tributary. There was once a time when water also flowed through here and into the main tributary farther on. This picture looks quite similar to the previous one except the plant life is not as tall or as abundant as in the previous picture. Also, if you look toward the top of the picture you can see what looks like a narrow road. It is the trail that was made for people to walk on when observing the creek when it had water flowing through it.

Coal Mine Canyon, Coalinga, CA

The small town of Coalinga was born in 1891 when the Southern Pacific Railroad bought 160 acres of land from M.L. Curtis. Coalinga is located 52 miles Southwest of Fresno, and it has an elevation of 673 ft. Coalinga thrived from the coal mines and then thrived substantially from the second oil rush of 1890. Back in the late 1800’s there were (3) coaling stations, Stations “A”, “B”, and “C”. The name Coalinga is derived from taking Coaling with Station “A” to make Coalinga.

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E This picture is of the Coalinga Coal Mine. It is in Coal Mine Canyon. This was the front entrance to the coal mine when it was in operation. The idea of coal mining died out very fast and that is when the second “oil rush” started and Coalinga became a successfully striving small town.