Police say the investigation began when the teenager told a school counselor she was having sex with the firefighter at his apartment. Her name, and the name of her school, have not been made public.
Allison surrendered on February 4 after police investigated the girl's claims and searched his apartment.
The two-year firefighter has been placed on administrative leave pending the outcome of the case.
Murrieta Fire Chief Paul Christman called the allegations "unconscionable" if they are true.
A preliminary hearing has been tentatively set for March 28.
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