In 1841 Charles Wilkes of the U.S. Exploring Expedition wrote:

"... Eighteen miles below Wallwalla they passed the Windmill Rock, about which are a number of curious basaltic peaks. ..." [Wilkes, July 6, 1841]

William Henry Gray, in his history of Oregon from 1792 to 1849 (published in 1870) mentions Windmill Rock as he wrote about passing through the Wallula Gap.

"... Twenty-five miles above Castle Rock stands the thriving little town of Umatilla, at the mouth of the river of the same name, and nine miles above is Windmill Rock. In ascending the river fifteen miles from this place, the land on either side rises to some fifteen hundred feet above the level of the river which occupies the entire bottom from rocks to rocks on either side; when the land suddenly drops from this high plain which extends from the Blue Mountains on the east to the Cascade range on the west, forming, as it were, a great inland dam across the Columbia River, fifteen hundred feet high at the place where the river has broken through the dam. As you pass out of this gap, in looking to the north and east, the eye rests upon another vast, high, rolling plain, in the southeastern part of which lies the beautiful valley of the Wallawalla. ...     The most of this vast, high, rolling plain, and especially the valleys, have more or less of alkali soil; the high plains are similar to those we have just passed, --- destitute of all kinds of timber, except at the foot of the mountains, and small patches of willow and cotton-wood, in some little nook or corner, near some spring or stream. ..." [Gray, 1870]

"Castle Rock" is the now historic location of Castle Rock, Oregon, with Umatilla and the Umatilla River located upstream. Nine miles above the Umatilla River is located Hat Rock and Boat Rock. Perhaps one of them might be "Windmill Rock" ??? On the east side of the Wallula Gap is the Walla Walla River and the Blue Mountains, a spectacular view when heading east across the Gap.