This map appeared in the 1889 book, "A Report on Washington Territory," by W. H. Ruffner and published by the Seattle Lake Shore and Eastern. As part of the book, a large map showing the proposed line across the state of Washington was included.
As this part of the map shows, the line was to go through Waterville and past the head of Moses Coulee over towards the Grand Coulee to cross between the upper and lower Grand Coulee where the map is marked "Fresh Water Lakes." This spot became Coulee City a year later.
Other points of interest are Steamboat Rock, the towns of Douglas, Grand Coulee, Hazeltine, and on the far left the words "Island Rapids" which on another panel has the word "Rock" before Island Rapids.
This other panels of the map show the line continuing west through Wenatchee to a point over Cadys Pass (north of Stevens Pass) to a point near Everett, connecting with the Lake Shore line to Canada.
As proof for the line to Wenatchee, here is the next panel:
And the connection to Everett:
From the first panel shown, the proposed line east to Davenport:
And finally, the panel showing the as built line to Spokane:
Another more general map had this view: