The Eisenhower Tunnel tube opened to traffic on 3/8/73, which began the earnest progression of pushing I-70 further into Western Colorado.
The Eisenhower/Johnson Tunnels are the highest and longest vehicular tunnels on the US Interstate system.
The Johnson Tunnel tube opened several years later, in 1979, completing the Tunnel set.
https://www.9news.com/article/travel/eisenhower-tunnel-colorado-mountains-interstate-70/73-dfe24840-cc8b-47c3-8703-b65784681612