The arrival of hundreds of gold seekers in California during 1849 and the early 1850s actually was a second wave of invaders. The first intrusion started, not with James Marshall's gold discovery on the American River, but with Christopher Columbus.

Spanish missions brought European agriculture and livestock as they sought to convert not only the native peoples, but also the land. The colonial process that started with European explorers eventually spread through the Western Hemisphere, severely disrupting native life, ending at the Pacific Ocean, in California.

"California's relative isolation...proved insufficient as protection against these disruptive colonial invaders," William Preston writes in Contested Eden. It was, however, California's remote location that spared it for 277 years from "...the ravages of change that accompanied the founding of missions, presidios, and pueblos..."

Germs and other foreign organisms were the smallest invaders, and were accompanied by plants and animals, new to the California Territory, which found inviting habitats in the new land.

"The profound consequences that Old World life forms and lifeways had on California prior to 1848 were in part functions of contrasting environmental and cultural setting," Preston says. Old World weeds, for instance, proved to be not only able to survive ocean voyages, but to be highly competitive once they reached land. Parasites proved to be overwhelmingly destructive.

Although California was isolated by its position on the western edge of the continent, and by mountain and desert barriers to the east, the invasion was inevitable. The plants and animals that evolved in this isolation were at a disadvantage when confronted with new, vigorous species.

Early Hispanic settlers thought of California as a pristine wilderness and proceeded to "improve" upon what they found by bringing new plants, animals, and microbes. This approach came into conflict with the Indians of California and their established ways. They had learned how to react in harmony with the land, water, and life forms already in place. Settlers brought new challenges, many of which could not be overcome.

Most likely the change was underway when the first Spanish mission was built in San Diego in 1769. New weeds like curly dock, red stem, and prickly sow thistle were found in the adobe bricks of early missions. In the mid to late 1700s California saw the arrival of foreign settlers introducing new species of livestock and crops. Exotic new plants spread like wildfire across California's grasslands, taking over. Wild oats, ripgut, mustard, and filaree quickly became dominant, at the expense of native grasses.

"The replacement of native grassland species by invasive flora seems to have occurred first on the south and central coasts and then spread into the San Joaquin Valley," William Preston writes. "By the time of the Gold Rush, the invasive Mediterranean annuals were penetrating the Sacramento Valley and the coast north of San Francisco." Eventually these small invaders would take over 50 to 90 percent of California's grasslands.

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Copyright Don Baumgart, 2008