End of historic US highway 164 [II]

US 160 originally went northwest out of Cortez. The segment of modern US 160 between Towaoc CO (south of Cortez) and Teec Nos Pos AZ wasn't completed until about 1962. (Before that, the only access to the Four Corners monument was via a primitive road heading north from Teec Nos Pos.) When that highway was opened to traffic, the segment that branched off US 666 near Towaoc was originally marked as state hwy. 40. The road passed through the very northwest tip of New Mexico and then into Arizona as SH 364. It connected at Teec Nos Pos to AZ 64 (which itself had only recently been paved). So it's easy to see why those three state DoT's would've wanted to unify their new route with a single designation. In 1966, it was assigned the number 164 (that was the second time that route number had been assigned; you can read about the original US 164 on this page). Here's a map from that timeframe:

CDoT, 1968

The routing continued west from Teec Nos Pos via AZ 64, and it was co-signed with US 89 down to US 66 in Flagstaff (you can view photos from there on this page). The east end of US 164 was at US 160 in Cortez (you can view photos from there on this page). But the route was very short-lived: in 1970, when US 160 was rerouted to go southwest out of Cortez, it swallowed up the entire standalone section of US 164, so that designation became superfluous and was decommissioned.