Millions of people from around the world make their way to Yellowstone National Park every year to relish in its natural beauty, epic wildlife scenery, and rambunctious hydrothermal activity. But as park archivists are quickly learning, not everyone leaves with what they came with.

Last month, the normally docile hot pool Ear Spring spat out water, along with some human litter, in its largest eruption since 1957. Now, park employees are working to catalog the items “coughed up” by the geyser, including a pacifier from the 1930s, a cement block, dozens of coins, plastic eating utensils, and aluminum cans – all items that ended up in the spring either by accident or intentionally.

“After Ear Spring erupted on September 15, employees found a strange assortment of items strewn across the landscape around its vent! Some are clearly historic: they'll be inventoried by curators and may end up in Yellowstone's archives,” the park wrote in a Facebook post.

Park officials say they used “hand-held grabber tools” to collect the items, including a sign that looks like it’s “for a bear management closure” and a funnel-like item that can be explained by the amount of scientific research that happens in Yellowstone, especially around the hot springs.

“Perhaps a research team accidentally dropped it?” speculated the park.  

Located on Geyser Hill in the park’s Upper Geyser Basin, Ear Spring spewed water to a height of 7 to 10 meters (20 to 30 feet). The eruption was so strong that overnight it resulted in the formation of another feature located under the wooden walkway, meaning the area had to be closed to the public. With a temperature reading of 104°C (220°F), the feature is “pulsing water” and a 2.5-meter-wide (8-foot) area of the ground surrounding the hole is “breathing”, rising and falling about 15 centimeters (6 inches) every 10 minutes.

“[Park] employees and geothermal experts continue to monitor and collect data in this area,” the park wrote in an accompaniment to a video of the new feature. 

The US Geological Survey (USGS) reminds everyone that geothermal activity is normal in the region and that none of the new activity is worrisome (or indicative of the supervolcano’s impending doom).

"More than any single thing, I think the most beautiful part of Yellowstone is that it is a living system," wrote Facebook user CW Gross in a post last month. "It's a bubbling, roiling, erupting, heaving, rutting, birthing, growing, changing place. Other parks celebrate the beauty of what nature has worn away, Yellowstone celebrates the beauty of what nature is creating.” 

Of course, officials remind visitors that if you bring something into the park, you need to take it with you.

“Foreign objects can damage hot springs and geysers," the Park wrote. "The next time Ear Spring erupts we hope it's nothing but natural rocks and water. You can help by never throwing anything into Yellowstone's thermal features!”

Yellowstone National Park told IFLScience that until museum curators have had a chance to examine the items, they won't have any further information.