1. Graywacke sandstone boulders.

Much of Castro Valley stands on sandstone, and outcrops of it can be found throughout the area. Since most sand is made of quartz, sandstone is mostly quartz. Other “impurities,” such as clay, hematite, ilmenite, feldspar, and mica, add color to the sandstone. Iron compounds can make sandstone tan or brown. Sandstones with more impurities are called wacke or graywacke. Sandstone is a sedimentary rock formed from (not surprisingly) grains of sand (0.0625 to 2 mm in size). For example, over time, the sand in an old river delta or ancient beach becomes stuck together by much finer particles of quartz, calcium carbonate or iron oxide, sometimes produced from volcanic ash. An outcrop of sandstone can tell us a lot about geologic history, but typically few fossils are found in sandstone.

2. Dirt and soil.

Soil is easy to overlook. It’s common as, well, dirt. But soil isn’t just dirt. Soil is made up of many things. Most of it is minerals, broken up rock, clay, and sand. The key element is broken down living material, which comes mostly from decayed plant material. Living plants get their nutrients from the recycled plant and animal material and from the minerals in the soil.  

3. Grassy field.

The grassy lawn is not exactly a native California feature, but it is now its own environment. The grass is mostly Kentucky bluegrass (Poa pratensis) and fescue (Festuca sp.) with some crabgrass here and there.

   It’s easy to overlook grass, but the grasses are extremely important to us as cereal grains (wheat, oats, rye, barley) and animal feed. Unlike many plants that have the growing point at the tip of the leaf, grasses have the growing point at the base of the leaf. Thus, grasses can be grazed without hindering the growth and survival of the plant. The grasses evolved only 30 to 40 million years ago. Vast grasslands provided food for the rising age of herbivorous mammals which in turn provided the food for a variety of carnivores.

   In addition, there are several other small plants in the grass, including dandelions, plantain, and clover.

4. Blue and coast live oaks.

Coast live oak (Querqus agrifolia). (right) Several trees can be seen along the fenceline. This California native, evergreen tree has a short stout trunk and many crooked branches. It grows to a height of about 80 feet. The acorns have a thin egg shape and are an inch or so long and were preferred by the local Native Americans. They  removed the shells and ground the nut into meal. Then they washed them to remove their bitter taste and boiled or baked them for food.

Blue oak (Querque douglasii). (left) The blue is a native California tree. Its simple alternate leaves have a waxy coating that helps them retain water. They are about 1-3 inches long with wavy margins and somewhat blue-green from above and more yellow-green on the bottom. The trees grow in a twisted manner that makes them less desirable for lumber. They also grow very slowly. Native Americans used them acorns as food.

5. Casuarina trees (Casuarina cunninghamiana).

They may look like pine trees, but they are not. Originally from Australia and Polynesia, they are now planted as ornementals. Casuarina trees grow to about 60 feet. Their slender branches look a lot like pine needles. However, the leaves of the casuarina appear as small scales at the nodes on the branches.

6. Palm tree stump.

The stump is left from a palm tree. It is a mass of fiberous material. Compare this tree stump to the one in the Front Yard Area.

7. Other plants. Several other plants are found around the big rocks.

   Arborvitae (Thuja orientalis). Arborvitae is a common ornamental. It is a member of the cypress family. It has small (1/2 inch) cones at the ends of short twigs. The leaves this family are a rich source of vitamin C and were used by Native Americans and early explorers to prevent scurvy, a disease resulting from a lack of vitamin C.

   Privet (Ligustrum sp.) is widely used as a hedge and is in the olive family. The very small flowers appear in bunches. A dark-colored fruit is a favorite of birds, but poisonous to humans.

   Laurel (Umbellularia californica). This native of western North America, is similar to the bay laurel, whose leaves are used in cooking.