WARNING about the bugs! If you plan on taking this exact hike to the falls, it is apparently swarming with mosquitos. We did not go all the way to the falls because we were warned off by people coming the other way. While I didn't personally see the bugs, I certainly saw the dozens of red welts from the bites all over this guy's body. That was more than enough to convince us to turn around. There were no bugs to be found anywhere else in the area.
It's a little hard for me to rate this hike. As written, it's a pretty plain, uninteresting trail. It gets two stars because (as one local told us) you feel a little like you're part of an old western walking between the basalt rock walls of the coulee. We did it as the second part of our Frenchman Coulee adventure, and I would urge people to skip it and instead follow the trail we took for the first part. Referred to as the "Central Rib Trail" in John Soennichsen's "Channeled Scablands Guide", it follows the Sunshine Wall, to the tip of the wall, then down to the valley and the road, ending across the way from the small, gravel parking lot mentioned in the instructions here. It starts at the parking lot up the road. There are two where climbers park to camp the night, we started at the trail head in the one that has a pit toilet.
That rib trail is a narrow, rocky, sometimes a little hazardous trail with amazing views of Echo Basin and the (I'm assuming) dry falls that would have emptied into it. You can even see the indent that must have been the falls' splash pool thousands of years ago. On the day we went there were a lot of climbers taking advantage of the wall, and we were able to ask them for advice and directions when we had questions.
There is one narrow gap between a couple large basalt columns that is probably the only part of the trail that's difficult to find. Other than that, just take it to the tip of the wall and then descend back to the valley floor. We briefly considered following the wall around the tip, paralleling Vantage road, but the trail seemed to disappear. More daring adventurers may want to continue on to see what, if anything, is there.