if you use google satellite maps you can see a couple of houses beyond and to the left of the burm... so I can guess that someone is just slinging rounds or shooting at items on top of that burm and they are getting up into the private land.

roughly looks like 1300 feet from the google map. (roughly)

http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=lyons+colorad o&sll=37.0625,-95.677068&sspn=51.576045,67.236328&ie=UTF8&hq=&hne ar=Lyons,+Boulder,+Colorado&ll=40.171266,-105.458837&spn=0.012264,0.02459&t=h&z=16&layer=t%3 E