Trimountain #4 Cache is located at the hoisthouse. I walked in from the #2, but the new road shows there is another way. The crumbling pile of building across the road from the hoist is the shaft house. This hoisthouse is one of the better preserved in the area. It's thought that the large opening in the front allowed the salvage crews to remove the drum without destroying the building.
I started this series by driving in on 7th ave and parking at #2. From there I just walked up and down the roads to the caches.