The salt marsh harvest mouse is an endangered species found only in San Francisco Bay area. Uniquely adapted to its habitat, the salt marsh harvest mouse can drink brackish water and eat pickleweed. An important part of the food chain, the salt marsh harvest mouse eats vegetation produced in part by the sun, and in turn is eaten by many animals at the top of the food chain such as hawks and egrets.

Most of the mouse's habitat has been fragmented, leaving small parcels of salt marshes here and there, making it difficult for the mouse to breed and disperse. An important part of the recovery of the endangered salt marsh harvest mouse population is acquisition of suitable habitat. At Sunnyvale Baylands Park, habitat was created specifically to replace or mitigate for loss of salt marsh harvest mouse habitat elsewhere.