NEW EVIDENCE THAT THERE WAS ONCE WATER ON MARS -- NASA rover snaps photos of ancient 'waves' carved into Mars mountainside [livescience.com]
When the west was first being explored a large section of eastern Washington had badlands that looked like that and all the geologist knew is was the wind that caused the ground to look like it did. Didn't explain the big as boulders and huge potholes.
In the 1920s Geologist J Harlen Bretz first recognized evidence of the catastrophic floods and he was laughed out of room. It wasn't until flight allowed geologist to look down were they able to see is was a great flood that carved the Channelled Scablands.