When we visited yesterday (June 28th) there was a ranger in the booth at the entrance and the fee was $5 unless you have the annual America the beautiful pass.
It's $5. If you don't have cash or check for the envelope, there's also a sign at the trailhead with a QR code which takes you to a site that you may pay electronically using a card.
5.00 parking fee
It's a day use fee if you don't have the annual national park pass. Honor system with envelopes.
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