You can find interesting things sometimes by looking down. A small medal plaque on a sidewalk along Kalamazoo's Crosstown Parkway notes an important communication link right below your feet.

The plaque reads in part

AT&T

Transcontinetal Cable Route

In This Vicinity

The notice is likely to construction crews to avoid digging and disrupting this vital communications link

History of the AT&T Transcontinental Cable

AT&T began work on an interconnected cable system to link all of America in the 1930s. According to a Wikipedia article on the subject,

The initial system developed in the late 1930s had 600 voice channels, far more than could be carried by balanced pair carrier systems, and cheaper per channel for high-usage routes. This version was standardized as "Type L Telephone Carrier System" in 1938, abbreviated at "L-1" after further developments ensued. ... AT&T Long Lines built two coast to coast systems of L-3 as well as shorter ones connecting major cities, especially the big cities of the eastern United States, as a supplement to the mainstay microwave radio relay systems. Some were later upgraded to L-4, while others were simply overbuilt with a new L-5 system.

A map of early communication lines at Atlantic-Cable.com shows a cable passing through Kalamazoo on its way to Grand Rapids, at one time the northern terminus in Michigan.

atlantic-cable.com

BONUS VIDEO - Flooding Along Crosstown Parkway in Kalamazoo