Liberty Hill is obviously historic. In the 1920s it was the center of a strike called upon by the Industrial Workers of the World (IWW) which halted 90 commercial ships. This had disastrous effect on not only the economy in Los Angeles, but also the rest of the state, country, and world. Today, the Port of Los Angeles is the busiest and largest shipping port in the country. Liberty Hill is also home to fossils, which have been here way before the 1920s. The monument in which the plaque is on has many geological features including imbedded fossils. So what are fossils and how did they get imbedded in this rock? Refer to the diagram below and I'll explain what it means.
Step one indicates a living species of aquatic life. Usually, a small fish in the ocean. When it dies, it falls to the bottom of the sea floor. Over time, sediment that has been carried from the water itself start to sink to the bottom of the ocean floor as well. Because the fish is denser than the smaller particles of sediment, the fish sinks even further. Just like quicksand, but only this takes millions of years instead of a few minutes. Step two indicates that the fish is starting to sink into the bottom of the ocean as sediment is being piled on top of the fish. Step three indicates that the fish is fully submerged in the bottom of the ocean. The fish can sink down miles below the ocean floor, but this depends on a few things such as how large the fish is, or the type of sediment being deposited. The lower the fish goes, the hotter it gets. When it gets to a certain point below the surface, the fish literally starts to burn off impurities. By this point, all that is left are the bones as it has taken millions of years to reach this point. When the impurities are burned off, it leaves behind fossilized rock as seen in step four. A common misnomer is that fossils are bones, but this is not the case. Fossils are actually rocks that have taken up the place of bones of dead animals.
Now, I'm sure you're asking how do fossils make it to the surface? This can be answered by knowing that tectonic movements cause land to move. Land moves because of convection currents in the earth. Similar to when you cook pasta on the stove and you see pasta sink and rise in the pot. This is a natural process of high or hot temperatures want to go to low or cold temperatures. This is one of the laws of nature, that everything tries to balance out. High pressure goes to low pressure to find a balance. When this happens in the earth, we get cracks called faults. We all know about the San Andreas Fault, which is only about 60 miles from this location. This fault was not always here.
40 Million years ago (mya), there was a plate that doesn't exist today called the Farallon Plate. It collided with the North American Plate heading north east at about a rate of 2 inches per year. This plate had fossilized marine life and it was carrying it right to California. About 20-25 mya, we had the creation of the true San Andreas Fault. Because the Farrallon Plate was a convergent plate (meaning a subduction zone at the intersection of the North American plate) heading north east, it made the San Andreas a transverse (or slip-fault). This may not make a whole lot of sense, but think about it as if the Farrallon plate went all under the covers at bed time, but never woke up. The covers being the North American Plate. The entire Farrallon plate disappeared under the North American Plate where is kept going deeper and deeper into the earth's core where it was melted and fused with the current North American Plate. Most of the fossils were lost, but some, likely less than .01 percent were part of the new fault and a new plate. The new fault being the San Andreas and the new plate being the Pacific. Look at the diagrams below to get a mental picture.
TO LOG A FIND ON THIS CACHE YOU MUST GIVE ME THE CORECT ANSWERS BEFORE YOU LOG A FIND. YOU CAN CONTACT ME THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER. ANY INCORRECT ANSWERS WILL RESULT IN A DELETED LOG
1. Liberty Hill on the first line of your email.
2. Look very carefully for any fossils you see. They may not appear to be the same on in the diagram. Pick at least one you see, describe the (a) texture, (b) length in cm or in, (c) color, and (d) shape.
3. Describe the weathering these fossils have had since they have been placed here.
4. What place do you think this rock and fossils came from in the Pacific Ocean given it's type of fossils, weathering, texture, color, and sediment disposition? Did it come from a coal reef, an abyssal trench, the shore, ect. Also explain how you came to your conclusion.
Works cited
http://www.dmp.wa.gov.au/11881.aspx
http://www.sjvgeology.org/geology/tectonics.html
Caches with the 'Cruise Ship' photo
- are pedestrian friendly,
- within walking distance of the pier.
