The distance depends on the site you choose, but it's not more than a 5 minute walk. They have wheelbarrows at the parking lot for you to borrow to bring your stuff down. If you reserve 3 months in advance, make sure you're on the reservation site EXACTLY at 7am PST because the spots go insanely fast.
Reservations can be made 3 months ahead of time, to the date. The campsites are booked out with in a second. This is NOT a place to just swing by and camp -- it requires extensive luck and discipline to actually get a site. Kirby Cove Camp is a campground and scenic area managed by the Golden Gate National Recreation Area in the Marin Headlands, California. Thus, you can reserve it on the Federal site (recreation.gov) -- NOT the California site (reservecalifornia.com).
How's the fishing regulations. Are there or can you fish the area.
Getting a reservation is the most important thing on day one of the booking window because it is one of the most coveted spots. You're camping spot won't be that far from the parking lot like what Christine said above.
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