People have been riding and playing in those canyons for at least 3 decades. Hasn’t happened yet. But the security state is new and fun. Zee rules must be followed.
Besides, the guy who decided to be a prick in enforcing this could have been a homo in this day and age.
One significant difference between the past decades and now: If someone were hit with a ricochet, the Marines would be sued (and lose) for not properly marking the area, despite the fact that the signs were stolen. And, in our “modern” environment, they’d move heaven and earth to fry some young PFC for carelessly discharging his weapon.