It's funny to see a skate park so close to home. I play softball in a men's league across the way from it. This seems like a lazy solution that will be very hard to clean up after the fact though.
37 tons = 74000 lbs or 740 cubic ft
3 inches of depth gets you 4 sq ft of coverage
740*4 gets you 2960 sq. feet.
The city says the park is 14,000 sq feet. [1]
In the video you can see they avoided spreading it in a lot of areas because they didn't have nearly enough!
Conclusion: Sand is heavy
[1] https://www.san-clemente.org/Home/Components/FacilityDirecto...
If you've ever tried to pick up a sack / large bucket of any of these things, it's like that but even denser. Compound that by the usual "volume varies as the cube of a side" thing, and this gets really heavy fast.
I wouldn't be too concerned about cleaning it up afterwards - 90% can be dug out quite rapidly, the rest calls for half a dozen skaters with brooms or an industrial size vacuum cleaner. (Think: a trailer with a beefy diesel engine on it to power the suction pumps - I watched one clean out a drydock once. Never thought I'd find cleaning up a mess so fascinating.)