Estuary, Watershed and Shore

Forty per cent of all California’s surface waters flow through the Carquinez Strait and San Pablo Bay. San Pablo Bay is part of the San Francisco Bay Estuary, the largest on the Pacific Coast of the Americas. It reached its current size about 12,000 years ago due to sea level rise. Previously a river valley, it was filled as the Ice Age glaciers melted.  A mighty river had flowed through the valley from Carquinez to the Golden Gate from 620,000  years ago, when a wall of water from an ancient inland lake broke through the gap between today’s Crockett and Benicia. Then, the Pacific Ocean surface was 500 feet lower than today. 

Today’s sharp shoreline was defined in 1878 by the Northern Railway’s tracks. Before then, the shoreline from Point Pinole to Carquinez Strait was a series of marsh wetlands punctuated by low bluffs. From 1850 to 1930 San Pablo Bay itself was altered by the deposition of enormous quantities of silt produced by hydraulic mining for gold upstream in the Sierra foothills. 

The watershed of Refugio Creek runs upward from the San Pablo Bay about three miles southeasterly to an elevation of about eight hundred feet.  

San Pablo Bay

Stand at the mouth of Refugio Creek, look north, and take in the view of ten miles across the 90...

Refugio Valley

Refugio is one of several creeks draining the low hills of Contra Costa into San Pablo Bay. It flows for...