Seems like there might be a case made for establishing NTC II down by the river. Terrain would fit the mission, no?
"To train America's soldiers for escalating global conflicts throughout the world, the U.S. Army operates extensive war game training exercises to simulate real world combat and ensure U.S. military preparedness in the 21st century.
Although these exercises take place throughout the world, the Army operates a first-class warfare training facility in California, designed to prepare Army units for desert warfare conflict.
Based in California's Mojave Desert at Ft. Irwin, the National Training Center (NTC) is the Army's premier combat training installation in the world, providing a realistic, desert warfare environment. This training environment, complete with a lethal and dedicated opposing force and significant maneuver space (more than 300,000 acres), allows Army units to sharpen their skills and focus by fighting the resident NTC Opposing Force (OPFOR)."
Seems to me like it fits all the basic reqs.
The Legions are fighting in Gaul and Germania, but our greatest enemies are walking in through the open city walls.