Yes, it can be an expensive day. Prices are $39.99 for adults and $29.99 for kids and seniors if you don't get a season pass. (Kids 2 and under get in free). Worth it. And much cheaper than a trip to the pool store. The first time we drove out to the West Valley park, we had no doubt the kids would have fun. What we didn't know is that the place is a joyride even for older, ex-skydiving adrenaline junkies like us. Of the several big-time slides, Mammoth Falls gives us a rush every time. You sit in a four-person raft that, once leaving the station, lurches down a steep flume, rushing toward a 50-foot wall. It has two "oh, bleep" moments — the initial drop, then the out-of-control feeling on the weightless apogee after inertia carries the raft up that wall. But — ha! — we and our kin somehow don't fall out of the raft. The sensation is all part of the design. Our oldest child now enjoys this feeling almost as much as we do, but we're both still young enough to have fun in the wave pool, which has a sort of undulation mode that creates an unending succession of body-tossing waves. Our younger kid doesn't like the big slides but has spent hours in the wave pool, kids' splash area, and wading pools, which makes us feel great, too.