Casimir

Have a circle of redwood trees off our deck that we'd like to place a new hot tub in the center of. Trying to determine the best base to use. The ground is fairly uneven, but don't want to dig down much to level, and risk damage to the root structure. A thick layer of compacted gravel vs. pouring a concrete slab? In central california, so minimal freeze/frost heave risk, but moderate amount of winter rain. Thank you