The San Francisco Bay
This lesson focuses on San Francisco Bay Estuary. Students will learn the
importance of the bay.
The waters of the San Francisco Bay are a mixture of the salt water flowing
in from the Pacific Ocean, and the fresh water rivers that feed into the
bay. The water in the bay is neither salty or fresh, but brackish. This
entire system is known as an estuary. The San Francisco estuarine system
is made up of three bays: San Francisco Bay in the south and San Pablo
and Suisun Bay in the north.
The San Francisco Estuary is a very dynamic system that constantly changes.
The geology of the bay gives us clues that the system has changed through
time. Mountain ranges surround the bay. The movement of the plates under
California caused this series of hills and valleys. The bay, located in
one of these valleys, was created about 2 million years ago. After the
Pleistocene glaciers melted (15,000 to 18,000 years ago), this valley flooded.
During this time, the Sacramento and San Joaquin Rivers must have flowed
through the Golden Gate, eroding a very deep channel. The San Francisco
to Oakland area was probable a flood plain with broad river beaches. In
the stream valleys roamed now extinct species of camel, horse, bison, ground
sloths, and saber tooth tigers. Fossils now found on Mt. Diablo, San Ramon
area and Irvington, Fremont area are proof that these animals once lived
in this area.
Salt marshes of the San Francisco Bay area are highly productive and extremely
valuable to the bay's ecology. Salt marshes contain a variety of plants,
but there are only a few common to all California salt marshes. Some of
the most common plants found in the salt marshes include:
Salt bush - a low-lying shrub that can tolerate salty soils
Salt grass - long and narrow grass leaves, about a foot in height
Cordgrass - dies in the fall, but can tolerate many hours of submergence
in the marsh water, filters salt out of its leaves where the salt crystals
can be seen on its leaves
Pickleweed - stems that are pickle-like in appearance, absorb salt into
their stems giving them a 'puffed-up' appearance, eventually these 'pickles'
dry up and fall off
Animals of the Bay
A large variety of animals live in the San Francisco estuarine system.
Mammals, birds, reptiles, amphibians, invertebrates, protozoa, and fish
all occupy a place in this system. The system has many parts because of
the need for larger animals to feed on the smaller animals. This food chain
gives us clues of why animals eat and live where they do. Many organisms
depend on the bay for food, safety, and shelter.
4-6 Watershed Curriculum Next
Print out a copy of the San Francisco Estuary map choose either html
version or pdf version for each student.
You may also wish to make an overhead copy of this map, or bring the map
up for the students to see using a computer presentation system.
Introduce the students to the San Francisco Estuary system using the background
Point out the three different bays within the system.
Locate the main bridges of the bay. (Oakland-San Francisco Bay Bridge,
Golden Gate Bridge, San Rafael-Richmond Bridge, San Mateo Bridge, Dumbarton
Bridge, Carquinez Bridge, Benicia Bridge)
Find the city of Fremont on the map. Ask the students to color Fremont.
Identify which bay Fremont's waters flow into. (San Francisco Bay) and
which bridge is nearest Fremont.
Inform the students that the salt marshes are located in the lower end
of the San Francisco Bay, all along the inside of the bay where Fremont
is located. Coyote Hills is one such protected area of salt marshes. Ask
students if they have ever been to Coyote Hills and seen the salt marches.
Save this map for future reference.