The Monolith Monsters
(1957)

The Monoliths are alien crystals that grow hundreds of feet high...endlessly growing, collapsing and growing again as long as there's water around.

After killing dozens, the Monoliths are just about to escape the canyon and overrun the world when the scientists discover salt water will destroy them.

The valley is flooded with water from a salt lake it and the threat is ended.

Thanks Moore!