Selective colleges admissions are generally conditional on things like completing senior year with acceptable academic performance in previously reported courses.
However, it appears that many of them are not very specific on the academic performance condition, which is presumably why students slacking off in senior year come here with this same question year after year. It appears that UCs are outliers in specifying an actual senior year GPA threshold (along with other specific conditions like no D or F grades) for the student to have a “safe harbor” against rescission.