STILLWATER, Okla. (AP) — Two mothers unveiled the green highway sign on a June morning.

Moments earlier, members of a solemn crowd stood in the grass next to a parking lot and bowed their heads. Mike Chase, the director of Strode Funeral Home, delivered a prayer.

His steady voice carried above the roar of the vehicles passing the Ampride gas station beside Highway 33.

Then Robin Briggs and Anne Fultz untied the fasteners that held a cream tarp over the road marker.

Just more than 43 months earlier, Jennifer Briggs and Heather Wilson, Robin's and Fultz's daughters, respectively, traveled the hi...