Anyone know what's going on in Vegas 6/8-6/10?

I am helping my brother plan a trip from 6/7 to 6/10, but the rates are exorbitantly expensive for that weekend. And I keep seeing good offers on Groupon Getaways and things like that, but they are always blacked out for 6/8-6/10!! What gives? Any ideas?

Best info I've found is that the Electric Daisy Carnival is being held.........and everyone in the free world is apparently expected. I'm trying to book through the 8th and hotel rates go stupid high that night.

Thanks - that's probably it!!