Hinting at the past

As I walk around my home, I can see signs of the household's daily activities everywhere. From the shoe pile I know who's been out and surmise where they've gone. In the kitchen I can follow the proverbial breadcrumbs and deduct who has eaten and what they've eaten.

Even when I walk into a home for the first time I can see signs of life. The favorite sitting position in a room is made obvious by the well-worn cushions. The muddy print on the refrigerator door handle tells who was working in the garden. Our homes reveal endless clues sharing the history of our activity.

In a manner similar to the marks left in our homes, trees and plants leave hints to past activities. When walking amongst deep, thick chaparral I am always surprised to come upon an ancientlooking fruit tree, evidence that there was an old homestead somewhere nearby.

Other times I will notice an oddly growing plant that seems to have branches growing from only one side. Observing more closely, I see an old stump near the plant, opposite to the branching. This indicates to me that this plant was once shaded by this tree, causing it to reach out to the sun on only one side. Vestiges of cattails and stone walls tell me where still water once pooled, the tale of old cattle ponds.

Traveling back

Reading the botanical landscape shares not only what is happening now, but also the history of the land. With acute knowledge of place and plants you can travel thousands of years back to Native American heritage or millions of years back to the formation of California's topography.

To journey millions of years back in time using the plants, we must consider the relationship of plants and soil.

Soils are formed from the exposed geologic structures that make up California's topography, such as the transverse mountain ranges of the Los Angeles or the Sierra Nevada backbone of our state. Geologists classify these crustal rock formations into three broad categories- igneous, sedimentary and metamorphic.

Igneous is often referred to as fire-formed- rock becoming solid when molten magma is cooled, such as granite or basalt. Rocks formed by extreme compression are referred to as sedimentary rocks, like conglomerates, chert and sandstone. And metamorphic rock, including marble, schist and serpentine, is formed by extreme heat and pressure.

Minerals make the soil

Each type of rock is made up of a crystalline lattice ordered by its mineral components. When broken down, these mineral components become the nutrient-rich soil necessary for plants to thrive. Minerals are released from exposed rock by the process of weathering. Both physical and biological factors contribute to this process.

Sources of physical weathering are temperature differentials, water charged with weak acids, and/or wind. Biological weathering is caused by colonizing organisms such as mosses, lichens and flowering plants living on the rocks. Weak acids produced by their metabolism serve to "eat" away at the rock.

As the rocks are broken down into smaller and smaller fragments, soils are formed and minerals are released. The minerals are composed of different elements, such as potassium, calcium, magnesium, sodium, iron and silicon. These elements usually form compounds by joining with oxygen or sulfur.

By analyzing soil types for mineral composition, one can better understand the underlying geologic features. For example, granitic soils will be high in silicates. Sedimentary limestone soils will have a high calcite composition. The bizarre serpentine soils are composed of chrysotile, asbestos, lizardite and antigorite.

Accordingly, certain plants prefer certain soils with specific mineral compositions best suited to their needs. By looking at the growing flora one can "see" the rocks below. For example, in igneous granitic soils oakpine vegetation thrives, but this vegetation will change dramatically as the soil gives way to serpentine minerals which support chaparral habitat dominated by Ceanothus sp., manzanita and coffeeberry.

By reading more deeply into the plant life a rich tale of California is told. The plants reveal the evolution of the land as well as the history of human activity, giving me a better insight of my place. Similarly, by reading the signs in my own home, past the surface, I am able to gain more authentic appreciation for those I love.

Meghan Walla-Murphy can be reached at the following e-mail: mwallamurphy@yahoo.com.