Armed with trash bags, rubber gloves, and an enthusiasm that visibly surprised several adult bystanders, roughly sixty students from St. Paul’s Middle School descended on Riverside Park Saturday morning for the school’s annual Community Service Day — and by noon had collected 47 bags of litter, replanted three garden beds, painted two park benches, and unearthed a collection of items that the city’s parks department has described as “genuinely baffling.”

Among the discoveries: a fully intact garden gnome with no explanation, a typewriter in working condition, one left shoe in size 14, a framed photograph of a golden retriever wearing a graduation cap, and what appeared to be an entire chess set buried approximately four inches underground, with the pieces still arranged mid-game.

“We don’t know whose it is,” said eighth-grader Carlos Nguyen, carefully holding up a ceramic bishop. “But whoever left it, they were losing.”

The volunteering event, organized by school counselor Ms. Patricia Osei and parent volunteer coordinator Linda Webb, drew students from all three grade levels and was divided into four work stations: litter pickup along the main trail, garden restoration near the east pavilion, bench painting by the duck pond, and what was listed on the sign-up sheet as “general beautification,” which turned out to mean pulling weeds for two hours.

Sign-ups for the weed station were, predictably, sparse.

“I thought ‘general beautification’ sounded exciting,” admitted sixth-grader Amara Collins, yanking a dandelion out of the ground with considerable frustration. “It was not.”

Despite the deceptive job title, Ms. Osei said the students worked with remarkable dedication. Even the bench painting crew, which ran into difficulties early when seventh-grader Noah Park sat in a freshly painted bench and had to be driven home by his father, recovered quickly and completed both benches in under three hours.

The benches are forest green. Noah’s shorts are also now forest green.

At the garden restoration station, students planted marigolds, lavender, and what the bag labeled as “wildflower mix” but which Ms. Osei admitted she had purchased on clearance without checking the species too closely. Parks department horticulturist Janet Flores reviewed the planting afterward and said the garden looked lovely, then quietly removed two plants she did not recognize.

The highlight of the day, students agreed, was the discovery of the buried chess set, which sparked significant debate about its origins. Theories ranged from “someone buried it on purpose as a time capsule” to “a squirrel did this somehow,” with the squirrel theory gaining unexpected traction among the sixth-graders.

The chess set has been turned over to the parks department lost and found, where it joins the typewriter, the gnome, and the graduation photo — all of which remain unclaimed.

The golden retriever in the photograph has not been identified.

Ms. Osei called the day a complete success and said St. Paul’s plans to return to Riverside Park next fall. The parks department thanked the school for their efforts and asked that students please not dig unless specifically asked.

The gnome is currently on display in the main office.