Wallula Gap with highest flood overflow channel marked with blue on the left upon which the lake level projection is based.
Islands formed for brief periods along the fist anticlinal ridge south and west of Kennewick
Snipes Mountain a ridge within the Yakima Valley west of Sunnyside and east of Granger stuck up above the water in this scenario.
The water backed up the Yakima River including through Union Gap forming a pool in what is now Yakima and perhaps a small pool north of Selah Gap. The flood matches fairly well the inundation in the Yakima area.
Water also backed up the Snake River canyon all the way into Idaho on the east of the above map. Keep in mind water from Lake Missoula was likely still poring into the lake from the north. The river north of the Snake is the Palouse and its old channel, now Washtucna Coulee. That sharp canal-like line connecting the Palouse to the Snake is the current route of the Palouse as it follows a joint carved by the flood (the-palouse-river-leaves-its-valley). The back of water portrayed in the image is matched by thick silt units that fill the valley of the lower Tucannon River, a tributary that flows into the Snake from the south.