You'll probably need both shorts & jeans! Weather can vary quite a bit at this time of year. I've been there and it was probably 60's high and I've been when it was 80 for the high. Nights definitely get cool(40's and even rare 30's)so pants/warm jacket would probably be welcomed in the evening. Not sure where you're coming from, but as I'm from New England so I almost always try to wear shorts, no matter what, and even get in the pool as I know it's going to be a lonnnggg time before I do that again!