OK, found the study I remembered. Attached is an excerpt.

In this issue of Engineering News, Gen. Henry Chittenden, of Seattle, describes the project which he has worked out with much painstaking detail for building a railway tunnel 30 miles in length under the main range of the Cascade Mountains. The building of this tunnel would enable the railway traffic between Puget Sound ports and the interior, which now has to be lifted vertically to an elevation of 2,500 to over 3,300 ft. in crossing the Cascade range by the present railway lines, to pass under the main range at an elevation of only 1,200 ft Forgot to catch the date, might have been 1916 - well before design/construction of the present tunnel was started.