For the purposes of the California Penal Code, "larceny" simply means "theft". In other words, any place the word "larceny" appears in the Penal Code, the word "theft" can be used in its place.
For that reason, "petty larceny" means the same as "petty theft" and "grand larceny" means the same as "grand theft". Cal. Pen. Code s. 490a .
For specific definitions and punishments for those crimes, please refer to the specific pages for those types of theft.