Did you know this was a thing? I have lived in or very near Washington State for almost 30 years and I did not know this was a thing. Somebody on Reddit mentioned that the Palouse is one of these 7 wonders and I grew up near the Palouse so I decided to do a little research.
The first thing a learned when I started reading up was that there appears to be some confusion as to what the actual 7 wonders are with some sources replacing the Palouse with Hurricane Ridge in the Olympic Nat'l Forrest. So for the sake of being thorough I will cover all 8. I do like to imagine a bunch of people getting into fistfights over whether or not their local attraction is on the list.
The Palouse
The Palouse is a region in SE Washington characterized by gentle rolling hills covered in wheat and barley. The hills were formed over tens of thousands of years from wind-blown dust and silt, called loess forming like sand dunes. The soil is very rich and the scenery is pretty unique. Check out Steptoe Butte for tourist options. It kinda looks like the old Windows XP wallpaper but that was Sonoma Valley I think.
Mt. St. Helens
Mt. St. Helens has the distinction of being the only volcano in the contiguous 48 states to erupt in modern times, qualifying it as the 2nd wonder of Washington. When the north side collapsed it created the largest landslide in recorded history. On a side note my best friend was born at the base of that mountain 6 days before it erupted and had to be evacuated in a cardboard box. His parents had a car seat but they didn't like him that much so he got the box. I think it used to hold kitty litter. There are a bunch fascinating documentaries about that if you are interested.
Columbia River Gorge
It is a very impressive thing to see a river flowing through a mountain range and that is what Columbia River does in the Columbia River Gorge. You might have thought it cuts through the mountains but the river was actually there first. The earth's crust lifted to create the cascades but it happened so slowly the river was able erode away its path without being blocked. If you are a hippie wook the Gorge is also a great place to catch a phish concert. They also play good music there I just wanted to trash on Phish.