Ordinance can pop up with no warning. In the 1980s, workers building the new community of Rancho Santa Margarita, Calif. started turning up small bombs and rockets. None exploded, but bomb squads from a nearby military base were called out to collect and detonate them.

By 1991, cleanup crews had removed close to 61 tons of suspicious material from the area.

An airborne view of the target range at Plano Trabuco, Calif. in 1945 shows a ground target laid out at center foreground.

Locals thought the problem was cleaned up, but in 2003, contractors building a bike trail turned up several more bombs and rockets. Construction was halted, and 11 items (none found to be explosive) were discovered by a team supervised by the Corps of Engineers.

The area continues to be monitored, and local people are regularly warned to call 911 if anything suspicious turns up.
The Army Corps of Engineers is involved in a number of similar survey/cleanup operations across the country and is the supervisory agency if new sites are found.

More information: www.trabuco-bombrange.com. A list of U.S. danger sites is available at https://uxoinfo.com.