There's actually a story behind this rest area. It's particularly big: over 40 acres! According to the Oregon Travel Information Council: "Constructed in 1966, and as part of government’s awareness (sic) of the Cold War era, French Prairie’s location and size made it a perfect venue for staging military operations. Only a short distance from Portland Metro, and with the potential to accommodate rapid military vehicle deployment, the rest area was considered an optimal civic response tool. Large tanks and aircraft might have used the grounds or the Interstate to transport armed forces or emergency personnel."