The installation is an Army Reserve training area, and I'm going to guess it was a rifle range, rather than an artillery range.
Per here:
The cannon was aimed at some water containers, but the shot missed the water, tore through a cinder-block wall, skipped off a hillside and flew some 700 yards east, right into the Tassajara Creek neighborhood.They aimed at the hill, which probably serves as the backstop for the rifle range. Rifle bullets will safely embed themselves in the hillside.
They did not understand the concept of "elastic collisions" and did not anticipate that the cannonball, upon hitting a slope, would BOUNCE like a billiard ball up and over the hill, nor how much kinetic energy the cannonball would have. The Mythbusters guys really need to have somebody familiar with this stuff that they can call and talk to when they try things with projectiles.
Instead the cannonball flew over the foothills surrounding Camp Parks Military Firing Reservation, before spiraling back toward Dublin like a cruise missile.
Apparently the author of the article flunked high school physics.
That was a statement from County Sheriff J.D. Nelson, who has been a bomb expert on Mythbusters many times. I would bet that he was there on the range with them for this shoot as well.