The Argo Tunnel was started from its southern terminus at Idaho Springs in September 1893 .
The Argo Tunnel was reached its final length of 4.16 miles ( 6.69 km ) in November 1910 , after several pauses in the work .
The Argo Tunnel was started from its southern terminus at Idaho Springs in September 1893 , and reached its final length of 4.16 miles ( 6.69 km ) in November 1910 , after several pauses in the work .