PLACER COUNTY, CA - A mysterious force appears to be at work alongside Highway 20 between Truckee and Nevada City where the water in a Pacific Gas & Electric canal seems to violate a basic law of nature.
PHOTOS: Does the water flow uphill or downhill?
To westbound travelers, the sight is unavoidable and startling.
"You always see that canal and it looks like it's going uphill," said Laurie Stevenson, who was kayaking on nearby Lake Spaulding, the source of the canal.
Roughly four miles west of the Interstate 80 junction, Highway 20 crosses the canal and continues downhill while the canal appears to rise uphill to the left.
"No, you're not crazy. A lot of other people have noticed it too," said Bob Suter, who was fishing at the lake and chuckled when he was asked about the strange sight.
Water in an open canal cannot flow uphill, of course. The Highway 20 spectacle is an optical illusion.
A carpenter's level placed on the concrete wall of the canal confirms the water is actually behaving the way it should. The grade is slight, but definitely slopes downhill.
The phenomenon occurs in various places around the world, often called a "magnetic hill" or "gravity hill."
It typically involves the unexpected flow of water in an open body of water or the unexpected force of gravity on a car placed in neutral.
The brain takes its mistaken cues from the surrounding terrain where the horizon is often obscured.
"It's the eye tricking the mind," explained Eric Tucker, who said he's enjoyed the sight for years.
At the Magnetic Hill theme park in New Brunswick, Canada, visitors pay a fee to feel the sensation of their car rolling "uphill" on a short stretch of a former provincial highway.
Other examples include Gravity Hill in Pennsylvania and Gravity Hill in Washington State.
The spot where the PG&E canal crosses under Highway 20 is not included in any published lists of gravity hills.
It is unmarked other than a single sign warning of the danger of the swift and cold water, but there's no mistaking its existence.
John Goodman, who frequently travels Highway 20, said he enjoys taking out-of-towners past the canal.
"It's great fun to take someone there and say 'how do you think the water's going uphill?'"
By George Warren, GWarren@news10.net