On a Sunday morning in March, I lugged my bike to the park for an early morning ride. I arrived as the park opened. The entry fee ($10) is cash-only and on the honor system, so I filled out the envelope and put the only $7 I had in the envelope. I still have the receipt in my car and one of these days I'll get around to sending the other $3.
Many Vegas tourists probably never see some of the wonders they can find not far from the strip. Of course, the Hoover Dam is close, and you can do the Grand Canyon in a day-trip. But there's a lot more to explore off the strip. Valley Of Fire is one of those places you should try to see.