Hold onto your hat the next time you’re in Yellowstone National Park or it could become a part of the Yellowstone geology team’s growing collection.
With more than 300 retrieved, estimated to be worth more than $6,000, the hats are just part of an array of litter they’ve gathered so far in 2025, according to a recent report from the U.S. Geological Survey observatory.
As part of Yellowstone’s Geology Program, the crew remediates, studies and protects the park’s geology and hydrothermal features.
Hydrothermal area cleanup is one of the main jobs for the team, and the crew has collected more than 13,000 pieces of trash and 4,000 rocks and sticks to go along with the plethora of hats so far this year.
In doing so, they’ve traveled 1,300 miles of trails and boardwalks on foot and have driven more than 11,000 miles to reach the various thermal areas.
Rangers attempting to clean trash out of Morning Glory Pool in September 1975. (Dan Ing, National Park Service) 
Yellowstone National Park Geology Program team member Mara Reed uses a long grabber pole to remove a park map, presumably blown from a visitor's hand or pack by the wind, from a feature in Upper Mammoth Terraces. (Samantha Hilburn, National Park Service) 
A hat can be seen in Grand Prismatic in 2023. (Jacob W. Frank, National Park Service) 
Flying debris
Yellowstone's more than 10,000 hydrothermal features — hot springs, geysers, mudpots and fumaroles — continue to draw millions of visitors to the park every year.
The high traffic volume combined with strong winds leads to a great deal of unintentional litter such as flying hats, maps and more each year.
Items left in the hot springs and other features can cause significant damage and must be removed. So in comes the geology team.
They come from a range of earth science backgrounds from geophysics to volcanology to science education, and the red safety vests they wear make them hard to miss.
Along with all the accidental trash they have to pick up, there’s also intentional litter including sunflower seed shells, orange peels and other biodegradables which are “particularly time-consuming for the team to remove.”
Sticks and rocks need to be collected as well, and while some fall in naturally, many near boardwalks and trails accumulate when people throw them into the features.
Changing Nature
Anything thrown into a hot spring can forever change its behavior, as seen with the Morning Glory Pool, according to the USGS.
The pool was named in the 1880s for its resemblance to the blue flower and historic photos reveal the intensity of the deep blue color of the hot spring.
Today Morning Glory Pool looks completely different with more oranges, yellows and greens. While thermal features naturally undergo changes, researchers believe the color change to the pool was caused by accumulating trash.
“For many decades, visitors regularly threw garbage, coins and rocks into the hot spring, which earned the nickname the 'garbage can' in the 1950s,” said the USGS in a report.
The trash settled along the base of the vent, which restricted water flow into the pool. This lowered the overall temperature of the spring, which is one of the major factors that determines where different species of thermophiles (microorganisms that survive at high temperatures) can thrive.
In the hottest water temperatures, many types of thermophiles cannot survive and the hot spring appears a clear blue color.
As water temperatures cool, microbial mats often grow along the edges of hot springs with the orange and yellow hues now seen in Morning Glory Pool.
Realizing what was happening, rangers partially drained the hot spring and attempted to remove as much trash as possible in the 1970s, but their efforts couldn't reverse the change.
Left, an old sign and pile of coins in front of Morning Glory Pool in 1950. Right, Yellowstone National Park Geology Program volunteer Tara Cross smiles and shows off a pizza box found on Geyser Hill in Upper Geyser Basin. (National Park Service; Margery Price, National Park Service) 
Morning Glory Pool used to be clear blue in color, as shown in the historic undated photo on the left (National Park Service photo by Rentchler). However, close proximity to the road leading to Old Faithful (seen in the background of the photo on the right -- National Park Service photo by William Keller from 1965) meant heavy visitation, and tourists throwing so much garbage into the pool that the clear blue color was lost. (Public domain) 
Yellowstone National Park Geology Program team members Samantha Hilburn (left) and Margery Price (right), both Physical Science Technicians, pose with a snow pit dug near Lewis Canyon for installation of a semi-permanent GPS site, installed in collaboration with USGS scientists. (Dan Dzurisin, USGS) 
Morning light at Morning Glory Pool in 2022. (Jacob W. Frank, National Park Service)
Getting creative
The geology team has a creative collection of tools to reach the various items floating in the boiling water including grabber poles ranging from 2 to 12 to 30 feet, fishing rods or even extra-long slotted spoons.
They are trained to carefully traverse Yellowstone’s delicate hydrothermal areas to gather the trash, while also preventing damage to fragile bacteria mats and geologic formations. And along with the more typical debris they expect to collect comes a few unusual items.
“Favorite finds from the team during the summer of 2025 include a Birkenstock sandal, a pizza box with slices still inside, a fake Louis Vuitton bucket hat, a stuffed koala toy, a ball cap with the phrase ‘I Pee In The Lake,’ and a Polaroid picture of Excelsior Geyser which was found within Excelsior Geyser’s crater,” said the USGS report.
Data, Education And Much More
In addition to their trash collection, the crew conducts scientific research, gathering temperature data from hydrothermal areas using both ground-based and airborne methods.
By recording temperature at 30- to 60-second intervals, the data loggers provide indications of when geysers have erupted. Continually recording the activity of specific geysers is used to help predict geyser behavior.
They use water quality instruments to measure chemical composition of thermal areas.
Even more monitoring is done in collaboration with the Yellowstone Volcano Observatory, as they help install and maintain instruments that measure seismic activity, weather patterns and hydrothermal features.
There’s also hazard signage to install, footprints and graffiti to remediate and maintenance work in hydrothermal areas to supervise.
The geology crew also “assesses geologic damage or hazards in collaboration with law enforcement investigations and examines scientific records and resources to answer questions from other park departments.”
And when they’re not busy with all of those duties, members of the crew often can be found educating the public — talking with visitors along boardwalks and trails, teaching Junior Rangers about hot springs or explaining scientific concepts to tour groups.
So the next time you’re checking out Yellowstone’s unique landscape, secure your belongings and properly dispose of trash. This not only helps preserve the park’s beauty but makes the geology team’s job just a little easier.
