The title says "U.S. States with the highest average elevation," but the description says, "Name the states of the U.S. with the lowest mean elevation..."
I think I can give a better example... The tallest peak in the Appalachians is Mount Mitchell with an elevation of 2,037 metres (6,684 ft), which is lower than the average elevation of both Colorado and Wyoming as a whole.
Can someone explain the geography of why OR is here but WA is not but WA has Mt Rainier plus 49 other peaks above 8k ft and OR only has 33 above 8k? Is it because WA is larger and has more flatland, proportionately?
Oregon coastal range is a bit further west relative to Washignton's and the biggest reason is once you hit the coastal range in Oregon it doesn't get much lower. Except for the northern quarter of Washington the rest of the Washington gets back below 500 meters once you go east of the Cascades. It's a huge basin.
Not sure if it will work but, here is a contour map of the two.
Southern Oregon has the beginning of the Sierra Madres which continue into California. Washington lost the top of Mount Saint Helens. Oregon has a longer Coast Range while Washington has the Lower Columbia floodplain and the Puget Sound region. Oh and Oregon also has the Wallowa Mountains in the northeast.
Not sure if it will work but, here is a contour map of the two.
https://en-gb.topographic-map.com/map-99bg5k/Washington/?center=45.81349%2C-119.37744&zoom=6
As discussed in several comments above.