More than 20 West Marin residents over the past few weeks have been scammed by a debit card skimming scheme that police have traced to San Anselmo’s Gas & Shop, one of the cheapest and most popular gas stations in the county. In Marin, over 50 people fell victim to the fraud, which involves the use of a skimmer device attached to a pump’s card reader that swipes information stored on a card’s magnetic strip and steals pin numbers.

The Central Marin Police Authority, which is leading the investigation, obtained photographs from A.T.M. machines of two suspects withdrawing money from victims’ accounts at several banks. Police advise anyone who may have used a card at that gas station anytime in the last 60 days to check their bank statements, and, instead, to use cash or pay the cashier inside the station.

In West Marin, the majority of victims live in the San Geronimo Valley, where many residents use the gas station on a weekly basis. Jo D’anna, a Forest Knolls resident who was scammed, said she stops there each week.

“It’s the cheapest gas in just about all of Marin and anywhere, I think,” she said. 

Ms. D’Anna was scammed three separate times, leaving her out nearly $1,500—the average amount for most victims. Even though her credit union has pledged to refund the money, the loss drained Ms. D’Anna’s savings account and left her struggling over the long Martin Luther King, Jr., Day weekend.

“This is the money that I live on to supplement my social security,” she said. “This is a great hardship. It was a shock to have this happen.”

Police said this type of fraud is on the rise in Marin, Sonoma and Contra Costa Counties. Identifying skimming devices can be difficult, given the increasing sophistication of card-reading technology.

“It’s hard to protect yourselves against this kind of crime,” said Margo Rohrbacher, a Central Marin Police Authority spokesperson. “But when you go to use your card and see something odd—like a device sticking out of the reader—don’t use it.”