Groups gather for the Women’s March on Washington on Jan. 21. (Amanda Voisard/For The Washington Post)

Hundreds of thousands of people traveled to the nation’s capital last month for the inauguration and the Women’s March on Washington. In the weeks since they’ve left, more than 10,000 visitors have donated to local charities Metro SmarTrip cards that might have otherwise been discarded.

The idea to collect leftover SmarTrip cards started before Inauguration Day with a Maryland woman who participated in the Women’s March. Hilary Moore Hebert, 35, purchased dozens of the plastic cards and mailed them to a friend who was attending with a bus full of women from New Orleans.

Metro no longer sells disposable paper cards, and instead requires customers to purchase $2 plastic cards, with at least $8 preloaded.

Hebert asked her friend whether cards with a remaining balance could be returned to her, then posted to a Facebook group inquiring where to donate them.

People immediately chimed in, and word spread quickly: After the Women’s March, volunteers who learned of the Facebook efforts went to Union Station and the main charter bus parking lot at RFK Stadium to collect cards from people as they left Washington.

In all, more than 10,000 cards have been donated to the prominent D.C. charity Martha’s Table. Hebert said she is still receiving about 1,000 cards each week in the mail at her Maryland horse farm. She said donations have come from all over the country, including Hawaii. She is donating them to a handful of charities across the region.

“I’ve never seen anything like this before, where it’s just a bunch of strangers coming together, and by using social media in a really positive way,” Hebert said. “It’s something that seems so straightforward and easy, but it’s just something that hasn’t been done before.”

Ryan Palmer, chief external relations officer at Martha’s Table, said the nonprofit organization has never organized a Metro Farecard donation drive, nor has it extensively offered cards to clients.

Martha’s Table, which provides food, family and educational support to low-income D.C. residents, said it is sifting through the cards to determine the balance on each of them.

“We don’t put any restrictions on it,” Palmer said. “Transportation is expensive, hands down, whether you are trying to grocery shop, pick up your kid from school or go to work.”

It is unclear how many more SmarTrip cards might trickle in. The Women’s March on Jan. 21 accounted for Metro’s second-busiest day ever, with 1,001,613 station entries. The inauguration one day earlier saw 570,557 trips.

Hebert said people have also donated cards to D.C.’s Miriam’s Kitchen and the Virginia charity Doorways for Women and Families.

She said she wants to turn it into a sustained effort, eventually working with hotels to get their customers to donate Metro cards once they check out.

“Who would have thought that someone in Hawaii could help the homeless in D.C.?” she asked. “And that I could be sitting in a horse farm in Germantown and could end up raising tens of thousands of dollars for the city.”

Palmer said donated Metro cards are a novel idea for Martha’s Table. The organization will try to measure the effect of the donations to determine whether the initiative could be continued in the future.

“This was completely brand new to us,” Palmer said. “It’s really sort of evidence of what can happen when the community comes together.”