Can I collect unemployment benefits if I am laid off from an AmeriCorps position, which pays a stipend rather than salary/wages?

No, not if this employer did not pay you any wages and you had no other wages from any other employer. To be eligible in California, you must have received enough wages during the base period to establish a claim. Employers report wages to the EDD. The EDD then uses this information to decide if an individual earned enough wages in a base period to establish a UI claim.