Megaripples on West Bar...

on the Columbia River, south of Wenatchee, Washington, were generated by surging floodwaters from the mouth of Moses Coulee during the Pleistocene (click to enlarge):

A close-up view shows that the enormous bedforms sit on a terrace more than 150 ft above the present day river, and are 300 to 350 ft long and about 25 to 40 ft high.  The floodwaters are estimated to have been between 700 to 900 ft deep at this location during their deposition:

I snapped the images above on Wednesday morning, following my presentation the night before about the geology of Mars, where I compared them to similar sedimentary structures found on the red planet in Athabasca Vallis (click for larger image at higher resolution):

Image credit: MOC camera on Mars Global Surveyor, Malin Space Science Systems.