In a sedan no less. You don't need a four-wheel drive. Plus, driving out onto the beach is the only way to get close to see the sand dunes, unless you'd ready to hike or rent an ATV.
I think Oceano is the only state beach in California that allows you to drive your own vehicle out onto the sand. Highly recommend it — we didn't get stuck, and you just don't get closer to the water than that. We were there in early January, so we almost had the entire beach to ourselves. I imagine it is much more crowded in the summer time. What fun!
Helpful hints: Try to plan your visit as close as possible to low tide. Ask the park ranger about the creek crossing, too. There is a permanent sign that says you're not supposed to cross it, but apparently (according to the ranger) that is only during high tide.
Also, be sure — very, very sure — to drive only the dark, wet sand. (Not the white sand.) You may want to observe and see how other vehicles do it for awhile and ask the ranger plenty of questions before venturing out.
Some local residents stopped and showed us how to cross the creek. They also recommended we go skydiving. That is where we drew the line.
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