Bidwell Park in Chico CA has two 18 basket courses, one long and one short course. I played the long course a couple of months ago.
There are no concrete tee pads and the course is entirely natural with mansanetta bushes, scrub oak trees, lava rock, weeds, and dirt. There are no baskets but each pin has a pole with a gong on it. There are 3 pins that are parallel to 400' canyon which makes the view spectacular and you have to be careful not to throw too far right or you will lose your disc.
The course has a good variety of longer pin placements or shorter ones where you have to thread the needle of throw a flip or thumber over trees.
If you ever get a chance I would recommend that you try this course. There is another course in Oroville (18 baskets) that is supposed to be really nice, but the weather did not cooperate and I was not able to get out there.