http://admissions.ucsc.edu/publications/ap-ib-chart.pdf and http://admission.universityofcalifornia.edu/counselors/exam-credit/ap-credits/santa-cruz/index.html indicates that you need a 4 or 5 on an AP English test to satisfy an English composition 1 (C1) course at UCSC.
However, if you get IGETC certified, UCSC will consider you to have completed lower division general education requirements, which appear to include the English composition 1 and 2 (C1 and C2) requirements.
If you have more questions, you may want to ask UCSC directly.