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In my ’50s cruising days, after hitting Oscar’s Drive In on El Cajon Boulevard, one stop we would always make was at a “magnetic hill” where steel cans appeared to roll uphill. I believe it was called Merlin Drive, but it might have been somewhere near the beach. Am I remembering this right?

— Sleepless in Spring Valley

“Magnetic hills,” also called “gravity hills,” are a worldwide phenomenon, and San Diego has had its fair share of mystical slopes over the years. I don’t know if Merlin Drive (I assume you mean the road in Lemon Grove) ever had the reputation as a gravity hill, but it might have back in the ’50s. Nowadays, the best gravity hill in San Diego is actually a freeway off-ramp. If you exit 805 to Sorrento Valley and leave your car in neutral at the bottom of the ramp, you will roll back up the ramp while you wait for the light to change. It’s creepy.

Folksy origins for gravity hills usually involve some paranormal activity. A popular backstory used for a lot of them is that, 50/60/70 or however many years ago, a school bus full of kids stalled out on the hill and the children all tried to push the bus. Something went tragically wrong and all of the rugrats died horrible deaths beneath the wheels of the bus. Forever after, the ghosts of the children reach out from beyond the grave and push unwitting drivers up the hill. Other popular explanations involve “gravitational anomalies” that somehow negate the attraction between physical bodies; and that’s a quantum mechanical attraction, not a Tom Jones kind of attraction, for all you dirty birds out there.

Sadly, there are neither ghosts nor strange attractors at work behind the gravity hill phenomenon. It’s just an optical illusion that makes the slope of the hill appear to run in the opposite direction. Usually, the miscue comes from a weird perspective on the horizon caused by a treeline, buildings, or something else that interferes with a normal frame of visual reference. It becomes impossible to determine what’s “level” by visual cues alone. In the case of the Sorrento Valley off-ramp, the road actually turns upward just a little bit at the very end of the ramp; but because of the swooping, curving geometry of the freeway system, it’s difficult to tell just by looking at it.

There’s another freeway segment that seems to defy gravity, but it’s not as well known to cars because nobody ever stops in the middle of the freeway to try rolling up a hill. The stretch of I-8 west between Descanso and the Willows Road exit is open to bicycles and many a rider is familiar with the “hill” that can be climbed at 25 or 30 mph with relative ease. If it’s not outright downward, it’s at least flat.

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Dave Rice Feb. 17, 2013 @ 5:27 p.m.

The spot I always use to illustrate this phenomena to friends is the Mountain Springs Road exit climbing the I-8 grade westbound leaving the Imperial Valley after a desert camping trip...if someone needs a bathroom break I tell them to make sure to pee uphill.


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