Dressy Casual- It is an outdoor, forest venue-high heels may be difficult! Also, it may get a little chilly in the evening, please plan accordingly. https://www.accuweather.com/en/us/idyllwild-pine-cove-ca/92549/month/2621907?monyr=5/01/2018
If your invitation says "and Guest," then yes, you can bring a date. If not, we would prefer it was just you.