Whomever was coloring the highway on some of these earlier maps, well... They were a bit sloppy. But this is a very close detail on a very large map. Anyway, the red line that is supposed to be the highway needs to be ignored, the actual road is there, though. The red line actually follow the later US 30 "water route" and the Interstate alignments fairly closely.
The original alignment almost certainly lies under the westbound lanes of the freeway east of Ruthton Point. Approaching Hood River, though, there was significant regrading and new road construction with the construction of the improved US 30 "water route," as seen in the 1957 map above. Most of the original highway wandered through the regraded area under the new highway and its frontage roads. However, it did swing north near the Columbia River Hotel and Wa Gwin Gwin Falls (though the creek itself was significantly re-routed with the regrades), and the outline of the original alignment seems to suggest itself in the curve of the buildings west of the hotel on the 1957 map.