Deer Park Monastery
Buddhist monastic community in San Diego county founded by Thich Nhat Hanh

Plum Village Monastery
Thich Nhat Hanh's home monastery in France

There are other sanghas practicing in the tradition of Thich Nhat Hanh in Southern California.
Visit these web sites for details:

http://iamhome.org/usa_sangha.aspx

http://www.esangha.squarespace.com/sangha-directory/