If you like being away from most of humanity, then this park is in your range. It's very poorly marked from the Indian Ocean Rd, the signs are pretty miniature. Just north of Green Head, you can turn onto Coorow Green Head Rd. or if you're coming from Jurien Bay, turn right onto Jurien Rd, then left onto Cockleshell Gully Rd.
Once on Cockleshell Gully Rd. you drive forever on an unsealed road, until the point when you feel like your vehicle may either fall apart, or you will go completely insane. At this point, you're almost there. The road in the park is sealed, so don't worry you'll get a bit of a break.
At the entrance, there's a board telling you how much the fee is, as well as envelopes to fill out and place your money in. They don't have any people working at this park, you're on your own. About 1/3 of the way into the park, there are some walking trails, they're a bit gravely but take you to some nice views of the mountains. We went in the early afternoon, and it was still deadly hot so you may want to pick your timing a bit better. I felt a little like bacon frying.
Another 7kms past the trail parking, there is a picnic area. Around here we got to watch a lot of emus running around, there are actually a lot of emus in the park. After finishing it's back out onto the road of misery, towards the next adventure.