Most of the UCs historically were explicit about what your senior year grades and GPA have to be (historically often 3.0 with no D or F grades, though UCSC has sometimes given more vague conditions like maintaining your previous academic performance). Read your admission offer carefully to see what the conditions are.
http://talk.qa.collegeconfidential.com/college-admissions/2122350-faq-rescission-of-admission-offers.html has some more general information on rescission of admission.