“In 1857, Lt. Edward Fitzgerald Beale, a Naval officer in the service of the U.S. Army Corps of Topographical Engineers, was ordered by the War Department to build a government-funded wagon road along the 35th Parallel. His secondary orders were to test the feasibility of the use of camels as pack animals in the southwestern desert. This road became part of US 66.[9]
Parts of the original Route 66 from 1913, prior to its official naming and commissioning, can still be seen north of the Cajon Pass. The paved road becomes a dirt road, south of Cajon, which was also the original Route 66.[10]
Before a nationwide network of numbered highways was adopted by the states, named auto trails were marked by private organizations. The route that would become US 66 was covered by three highways. The Lone Star Route passed through St. Louis on its way from Chicago to Cameron, Louisiana, though US 66 would take a shorter route through Bloomington rather than Peoria.
The transcontinental National Old Trails Road led via St. Louis to Los Angeles, but was not followed until New Mexico; instead US 66 used one of the main routes of the Ozark Trails system,[11] which ended at the National Old Trails Road just south of Las Vegas, New Mexico. Again, a shorter route was taken, here following the Postal Highway between Oklahoma City and Amarillo. Finally, the National Old Trails Road became the rest of the route to Los Angeles.[12] https://en.wikipedia.org/wiki/U.S._Route_66
A fews years ago I drove the “mother road” from Victorville, CA to Gallup, NM, before turning south and continuing the trip to Texas. Without going into any more history and information about the road, clicking on this link will provide the reader with a very good description: Route 66 From End to End
However I will provide the following information from the above website. The photo of the general store was take during the above trip.
“Probably no other road in the world hosts as many interesting and strange sights as Route 66. People say it’s part of the charm of the historic highway. If you’re planning a road trip down Route 66, here are some one-of-a-kind attractions you shouldn’t miss.
Hackberry General Store (Arizona) — Located at mile marker 80 on Historic Route 66, this general store is jam-packed with any kind of Route 66 memorabilia you can imagine. There are vintage gas pumps and automobiles out front, although it’s no longer a filling station. Inside you can shop for souvenirs or pick up some Route 66-branded root beer.” 
Rt 66 Gas station in Hackberry, AZ