Can the police in California seize your car (i.e. tow it from where it's parked) without a warrant?
This is allowed under the police's "community caretaking" function. See South Dakota v. Opperman 428 U.S. 364 (1976):
To permit the uninterrupted flow of traffic and in some circumstances to preserve evidence, disabled or damaged vehicles will often be removed from the highways or streets at the behest of police engaged solely in caretaking and traffic control activities.
Police will also frequently remove and impound automobiles which violate parking ordinances and which thereby jeopardize both the public safety and the efficient movement of vehicular traffic. The authority of police to seize and remove from the streets vehicles impeding traffic or threatening public safety and convenience is beyond challenge.
The legal basis for a Police/Sheriff in California to tow/impound a vehicle will be based on the California Vehicle Code (and not on federal case law). As an example, California Vehicle Code 22953 permits immediate tow of vehicles under certain conditions.
In addition, each City in California has instituted Municipal Codes which further protects the rights of Citizens from unlawful parking of vehicles which cause nuisance.
In addition to the CVC and Muni Code, each Police Department has its own policies which are complimentary to CVC and Muni code detailing how the police handles vehicle impounds.