If you want to do it legitimately and securely, it's probably a lot more expense and harder than you think for very little return on investment.
Even for the parking, you likely need commercial insurance and if they are mountain biking on your property, I bet the insurance company will be either denying you let them or making you have them fill out disclaimers while raising your rates.
If you add a campground, you likely need to meet state campground regulations for water supply, sewage disposal, etc...
If you are in a remote area and small, you might go illegal and fly under the radar. Sometimes that works for decades...but one trip & fall and someone else may own your property.