I got a chance to get up on the edge of Wallula Gap. Alas access is very limited due to private property. The expansion of big ag ownership with irrigation has resulted access limitations.
I have put up a fair number posts on Wallula Gap:
https://washingtonlandscape.blogspot.com/2014/06/ice-age-floods-dem-and-lake-lewis.html https://washingtonlandscape.blogspot.com/2011/04/wallula-gap-and-john-mix-stanley.html https://washingtonlandscape.blogspot.com/2011/04/wallula-gap-and-prime-farmland.html https://washingtonlandscape.blogspot.com/2012/05/sheep-in-vineyard.html https://washingtonlandscape.blogspot.com/2012/12/columbia-river-treaty-and-cover-photo.html https://washingtonlandscape.blogspot.com/2013/01/grand-canyon-and-wallula-gap-its.html https://washingtonlandscape.blogspot.com/2013/10/wallula-gap-geology-and-art.html https://washingtonlandscape.blogspot.com/2013/11/lake-lewis-and-wallula-gap.html