Biology Reference
In-Depth Information
Dozens of creeks tumble from the steep slopes of the Coast Ranges onto
the flatlands before merging with the bay. The water that flows between
their banks is a highway that connects the ecology of the uplands to the
tidal estuary. From the leaves and sediments that drift from hilltops and
valleys; to the animals that travel between the ocean, marshes, and land; to
the fresh water itself that helps shape the aquatic habitats of the estuary,
creeks are an integral part of the estuary's anatomy.
In the Bay Area, creeks typically begin within creases in the steep
slopes of foothills and coastal mountain ranges. These headwater zones
collect water from natural springs or ephemeral runoff from storms. Far-
ther downhill, beneath the shady limbs of tanoak and bay trees, creeks
gather seasonal trickles, then coalesce into true streams punctuated with
still pools, gravel riffles, and sandbars. As the land flattens, streams may
peter out into alluvial fans or pool into freshwater marshes filled with
sedges and touched by the brackish fingers of the tide. “The ecosystem
doesn't draw a sharp line between creek, baylands, and bay. There's a con-
tinuum where these blend into each other,” says Phil Stevens, director of
the Urban Creeks Council. Every individual watershed recapitulates the
design of the larger estuary, with the tidal marsh at the foot of each creek
acting as its own miniature delta, and each creek mouth serving as a mix-
ing area for salt and fresh water.
Colma Creek near San Francisco's airport. (Jude Stalker)
