"Where is it located?"
Basically between Lincoln and Bannock Streets and Colfax (call it 15th) and 14th Avenues. The State Capitol is to the east, and the City and County of Denver Building is to the west.
In the article, this shot (Denver Post) looks due east toward the Capitol
http://www.denverpost.com/wp-content/uploads/2017/04/420_marijuana_denver_2017_rj_28724.jpg?w=810and this shot at 0:17 in the video looks due west, toward the City and County Building
https://youtu.be/Rh_YuI7qlvEI figure there are four possibilities.
An anti-somebody(s) tried to make the organizers look bad, in which case it will have backfired if this comes to light. (Remember the uproar about the mess left at the pipeline demonstration?)
Somebody involved with the event did it to cast suspicion on anti-pot factions, in which case it will have backfired if this comes to light
A pure out-of-his-skull (drugs, booze, psycho?) individual(s) just went plain bonkers.
The organizers and their witnesses are lying about the park mostly being cleaned up when they left.
A hotshot journalist tried to make a mountain out of a molehill for column-inches, even though it was a normal partial cleanup operation which had to be carried into the next day.
It wasn't a hungry bear, although that's sure what it looks like when a critter raids the trash. :)
As of 5:30 AM MST I haven't heard of any surveillance videos coming to light. The park is quite large and mostly treeless, ans I kind of doubt there are many ordinary cameras which could have captured "whodunit." As I recall as of ~10 years ago, it's a pretty big unlighted area except for stray light from buildings, etc. I don't know how or whether the authorities actively patrol it at night. Most nightowl barhopping activity is pretty much further east on Colfax, and the PD is not very near, on Cherokee.
Kinda interesting from a possible "false, false, false-flag" viewpoint. :D
Terry