I visited the Dutch Hollow trail area of Wasatch State Park. It's a good area to ride your mountain bike on short or longer rides. For a much longer ride you could connect to the Pine Canyon bike park or the WOW trail. No toilet in the parking area. Parking for seven or eight cars.
Update 11/7/2023: when you're driving up the paved road to Dutch Hollow the road ends and that's where there are just a few parking spots. I went back recently and I now realize that just before the road ends on the right hand side is a dirt road that's about a quarter mile long and it leads to a very large area to park many cars or even vehicles with horse trailers. There is also a pit toilet in that larger parking lot.
I should also add that many of these trails are suitable for kids or beginner mountain bikers. There are signs and maps at many trail junctions that describe the difficulty level of the trail. Green for beginner, blue for intermediate, black for advanced riders.
When winter conditions are suitable they also groom these trails for biking on the snow with wide tire fat bikes.
As of November 2023 the fee to park is $10 or display an annual Utah state parks pass.