bethie is right...students at the Claremont colleges (
www.claremont.edu) have access to dance programs at both Scripps and Pomona. The programs are strong, with some very serious dancers, but there's also plenty of room (in both classes and performances) for less experienced or less committed students.
I've heard excellent things about Chapman's dance department, though I don't know how accessible it is to non-degree seeking students. Ditto LMU. Occidental has some student dance groups and some dance courses through the theatre department, but I don't believe it offers a major (could be wrong). I assume the classes are accessible, but offerings are comparatively slim. Might still be more than plenty.
Not positive what you mean by "small." The Claremont colleges have approx. 5,000 undergrads between the 5 of them (largest is Pomona with 1,500 and smallest is Mudd with 750ish); Oxy is 1500ish; LMU is just under 6,000 (undergrads); Chapman is just under 4,000 (undergrads). So, all small in the grand-scheme of things, but LMU and Chapman are still fairly sizable.