Wildwood Park field trip

Conejo Volcanics at Wildwood Park

The large boulders that surround the parking lot are from volcanic mudflows. This debris came along from a steep place due to the force of gravitational pull. This milkshake like flow of mud rock carried along the way big angular blocks of clastic basalt. You can see these now embedded in the large light gray breccia.

Lichen

This green moss material is fungus and algae. It happens to be mildly acidic and is able to break down the rock it inhabits. Chemical weathering of the rock allows the lichen to obtain their needed nutrients for survival.

Palm Trees

How do these trees appear in this non-native environment? The people of Thousand Oaks have been planting these trees plentifully, and their seeds have been carried away to be redistributed at Wildwood.

Spherodial Weathering

This beautiful rock is made from pyroclastic material. Water seeps into the cracks of the rock and chemical weathering occurs. This action changes the silicate mineral to hydrous clay; it expands breaking off into sheets.

Topanga Formation

This formation consists of mudstone, siltstone and other sedimentary rocks. There is a conglomerate rock entrance into and within the Indian Cave. This cave also displays clam and oyster shell fossils. How can these two distinct forms, sedimentary cobblestones and marine fossils, be found in the same location? There must have been a stream or river to round the large stones, but marine fossils can only come from the ocean. There must have been a location where the river and ocean came to meet, a delta. The river pushes the rounded cobblestones into the ocean and now you have a mixture of the ocean fossils with sedimentary rock. There is no more water today, because of tectonics at work. Compression and reverse faulting caused uplift and mountains were formed. How fascinating?

Bathroom and lunch break

Walking to the dike the trail narrows

Why does this occur? What is that funky smell? The trail narrows due to the dike. The wide trail is softer sedimentary walk and is easily carved by water. Where the dike is the rock is hard igneous stone, the water cannot cut this easily. When we walk to the dike there is an odor, a sewer order. It is from the sewage line that travels down to the bottom of the hill to the sewage treatment plant. Gravity helps to pull the sewage down to meet the plant, but in El Nino years pipes break and raw sewage is the terrible result. Now let’s focus on the light colored tabular body cutting vertically through the sedimentary beds in the cliff. This is a volcanic “dike”, formed from magma that was flowing upward along a fault zone, feeding lava to volcanoes up above. This is one of many faults that cracked and widened this countryside about 16 million years ago, as it was rifted away from the mainland. Notice that the rocks that make up the dike have a different composition from the surrounding sedimentary rocks. The dike is andesite mafic dark colored intrusive igneous rock. The rock surrounding the dike is mudstone and silt stone, sedimentary rock.

Paradise Falls

Why is there a waterfall here? What caused this to form? Why is there not simply a stream running through? The reason is the there are differences in the rock and mineral composition. Igneous minerals grow together and are tightly locked, so they are harder than the sedimentary rock. As the river cuts through the hard igneous intrusive rock it is a slow arduous process. But when the river cuts through the softer sedimentary rock gravity works on pulling the river faster down stream cutting all along the way. This softer rock is worn away much quicker and starts to fall, thus forming the beautiful waterfall.

White rock

Calcium carbonate turns into calcite cement and coats the sedimentary rock. Rain and groundwater are absorbed in the rock, the acidic level is strong enough to slowly dissolve the rock and the calcium carbonate comes to the top of the rock. The calcium carbonate begins to evaporate leaving the calcite crystals behind.