This is a report I wrote for my college class, Physical Geography.

 

 

The Sibley Volcanic Preserve is a unique and unusual park in Oakland, California. Roundtop, one of the highest points in the Oakland hills, is the extinct volcano that this park introduces. It may seem untrue, but the volcano was turned sideways by two East Bay faults. The park was named after Robert Sibley, shortly after his death in 1958. Sibley is dominated by grasses and bushes, anywhere you look, there will be grass. The birds are always more visible than the other animals, but you will smell the skunks and you might hear rabbits scurrying through the brush. There are many trees in the park, not as many Eucalyptus trees as there once were, but they are there along with Coast Live Oak and California Bay Laurel. The best way to observe this park is by taking the self-guided tour; eleven markers telling stories millions of years old.

Roundtop is a small peak in the Oakland hills standing at 1,761 feet. The volcano was born about 10 million years ago, under the waters of the San Leandro Reservoir, which is now the location of Tilden Park. Sediments from the lake settled over the lava deposits when the lava stopped flowing, and volcanic activity began again. In the birth of Roundtop, there were at least two violent explosions and eleven separate lava flows. With all the volcanic and sedimentary layers, Roundtop has become a favorite spot for local geologists searching for complexity (Margolin, 1974). Roundtop was a volcano because being on the Hayward fault, the action of subduction occurred. Subduction is when one of the Earth’s plates moves over another plate (Rosa, 2008).

Roundtop is now somewhat one-of-kind. Since it’s birth 10 million years ago, the Pacific plate dragged it north, while tectonic forces tipped the volcano onto its side. The Hayward and Moraga faults pressured the geological structure that encloses Sibley into a U shape (Slack, 2005).

There is a vast array of plants at Sibley. Hilltops are covered by tall, yellow grass. Slopes are taken over by large bushes. There is a small amount of Eucalyptus trees remaining from the forest in the 1970’s. In the more recent past, Roundtop was home to a prosperous Eucalyptus forest, until 1973 when many of the trees were severely damaged or killed in a winter freeze. Since that time, the majority of dead Eucalyptus trees have been removed and they no longer dominate.

The man who made eucalyptus trees a part of this park was Frank Havens. Havens was a turn-of-the-century millionaire and founder of the Mahogany Eucalyptus and Land Company. The purpose of this magnificent, hasty company was to blanket the Oakland-Berkeley Hills with awesome forests of eucalyptus trees. As Havens put it, eucalyptus was “the most valuable tree on the face the globe” (Margolin, 1974). After planting millions of eucalyptus trees it was found that the trees were useless and the project was abandoned leaving the Oakland-Berkeley hills blanketed with an unmanaged invasive non-native species.

This park might as well be bird heaven. Scrub jays, red-tailed hawks, great horned owls, acorn woodpeckers, and Steller’s jays populate the trees and bushes. Red-tailed hawks can often be seen hovering high above the ground in search of food. The holes in the grassy hills are homes of gopher snakes. Under the brush, brush rabbits are living and storing food. The real pests are the raccoons and skunks, living wherever they can, feeding on food scraps and anything else they can find. In the few ponds that there are, there are California newts and Pacific Tree Frogs (EBRP, 2013).

The self-guided tour helps people learn everything they want to know about Roundtop’s very long history. This was how I gathered my information while at Sibley. There are eleven markers that give basic information about the geological history of each spot. You start the tour having to split off to shorter paths in order to reach the markers. After a while, the markers can be seen alongside the path. I found that the quarry at the second marker was the most awesome spectacle in the park. This quarry is found on the north side of Roundtop’s peak. The Kaiser Sand and Gravel Company dug up many tons of rocks exposing the interior of the 10 million year old volcano. Inside the quarry is a massive chunk of basalt lava sticking out of the wall. Another interesting feature was at the ninth marker along the trail. Walking toward the marker, you will notice the path goes through a small canyon. A fault separates weathered basal conglomerate from a huge basaltic outcrop (Johnson, 2005).

The Sibley Volcanic Preserve is a unique display of ancient volcanic activity. If man had not been so quick to exploit this area’s natural resources, this park would not be nearly as interesting as it is now. Sibley is already a popular place for people to bring their dogs, but I don’t think they notice the massive history that they walk on almost everyday.