Marin County is a peninsula—to the west is the Pacific Ocean, to the south is the Golden Gate, to the east is San Francisco Bay. The land is pleated by hills, the tallest of which, named Mt. Tamalpais, rises sharply from the ocean to an elevation of 2571 feet. Its distinctive profile is recognizable from great distances. The nearest taller peaks are Mt. Diablo, 36 miles to the east with an elevation of 3849 feet, and Mt. Hood, 35 miles to the north east with an elevation of 2730 feet. The closest significantly taller peak is Mt. St. Helena at the north end of Napa County, 50 miles away.
The countryside is alternately wooded, shrubby, and grasslands. Prominent among the trees are coastal redwood, Douglas fir, several oaks, madrone, bay laurel, and tan oak. The dominant shrubs are manzanita, coyote bush, ceanothus, and chamise. Wildlife abounds, and varies in size from the mountain lion to the mouse. We were once visited for a few weeks by a bear who was exploring from his home base on the northern coast.
Most of the southwest of the county is comprised of a contiguous region of public lands—parks under federal, state, county, and district jurisdiction. Hiking, horseback riding, cycling, and camping are the main forms of recreation. The northwest section of the county is predominately agricultural with dairy and beef ranches.
The human population is largely confined to the eastern side of the county. The population increases very slowly, its growth is limited by the preference for undeveloped public open space and the lack of water.
The domestic water supply is fed by rain collected behind seven dams. Twice since I have lived here water rationing was instigated after a multi-year drought. It only rains in the winter. If we're lucky the rains begin in October and stop in April. Some years have a shorter rainy season.
We face a number of natural disasters besides drought: earthquake, flood, mudslide, and wildfire. There hasn't been a bad fire since I moved here, but the specter of the Oakland Hills Fire of 1991 hangs heavy over our firemen's heads, as we are no less vulnerable to that kind of destruction than Oakland.
The weather is generally moderate; the biggest influences are the heat of the Sacramento Valley, the channel of the Sacramento River, and the icy southward currents of the Pacific Ocean. These combine to create a lot of fog. The occasional high atmospheric pressure keeps the fog at sea. Summers infrequently get as hot as 100 degrees, while winters rarely drop below freezing. Winter usually begins in November and extends through February, with January the coldest month.
Marin is a beautiful place where it is easy to lose yourself in a wild landscape. That and its proximity to the business, cultural, and educational features of the San Francisco Bay area make it a wonderful place to live. But the high price of real estate makes it expensive to live here.
There is a good history of the area with a flood photo on the website of the San Francisco Chronicle.