This is especially so at Caltech. The small size of Caltech is intentional - it fosters an interactive, collaborative environment that is unmatched in the world of science. There are research programs throughout the campus that are of interest to chemists, and with the small size of the campus it is very easy to find them.
Chemists have active collaborations with biologists, physicists, geologists, and engineers.
And of course, chemical engineering and chemistry are in the same division and have a long history of fruitful collaboration.