USGS Corrected Century-Old Yellowstone Geyser Naming Error

Archival correspondence from 1926 revealed a decades-long misplacement of the Black Pearl Geyser sign in Wyoming.

Updated on Oct. 5, 2026 in Geology

Isometric editorial illustration of geometric mineral sinter deposits and steaming hydrothermal vents in a basin. — The U.S. Geological Survey has resolved a hundred-year-old naming error for the Black Pearl Geyser, following archival research into 1925 geological shifts in Yellowstone National Park. AI Illustration. Upload story photo >

The U.S. Geological Survey confirmed the resolution of a century-old naming error involving the Black Pearl Geyser in Wyoming's Yellowstone National Park. Researchers used preserved 1926 correspondence to trace the sign's misplacement to a hydrothermal explosion that occurred in 1925.

Why it matters

Identifying the error helps clarify the geological history of Biscuit Basin, where rare thermal features were obscured by the 1925 event and recent activity. Reconstructing these events improves the accuracy of mapping fragile sinter deposits that characterize the region's landscape.

The original sign was positioned 1,000 feet away from the actual Black Pearl Geyser, a feature defined by its dark, pearl-like spheres of sinter—a porous, opaline silica deposit formed by geyser activity. This error persisted following a 1925 hydrothermal explosion that destroyed the local sinter crust near the Firehole River.

The players

U.S. Geological Survey

The federal scientific agency responsible for monitoring Yellowstone's volcanic and thermal activity.

J.R. Van Pelt

A park ranger whose 1926 documentation provided the key archival evidence for the sign's misplacement.

J.E. Haynes

A historical correspondent whose 1926 letter corroborated the location error in Biscuit Basin.

The details

The correction relies on letters from 1926 written by J.R. Van Pelt and J.E. Haynes, which detailed the aftermath of an unobserved 1925 hydrothermal explosion. This event, which involved a violent release of steam and water, rearranged the fragile surface features near the Firehole River. By cross-referencing these accounts, researchers confirmed that the sign was incorrectly placed after the 1925 event shifted the landscape, creating a geographic disconnect that lasted for nearly a century.

1925: A hydrothermal explosion altered the landscape of Biscuit Basin.
August 15, 1926: Ranger J.R. Van Pelt wrote a letter about the sign error.
August 26, 1926: J.E. Haynes confirmed the signage error in a letter.
July 2024: A hydrothermal explosion occurred at Black Diamond Pool.
October 2026: USGS confirmed the reconstruction of the historical naming error.

The Tech Race

This analysis of historical thermal features follows the precedent set by the July 2024 hydrothermal explosion at Black Diamond Pool, which prompted a comprehensive re-examination of the area's shifting geomorphology. By reconciling historical records with modern observations, researchers aim to better track the evolving stability of the Biscuit Basin thermal landscape.

Visitors to Yellowstone’s Biscuit Basin should note that the physical location of the Black Pearl Geyser has been clarified to match its true geographic coordinates. This update ensures that historical and modern maps of the Firehole River area are now synchronized for current park navigation.

The takeaway

This correction underscores the value of archival records in validating geological site data after major thermal events. Residents and researchers can monitor the park's official hazard updates for any additional geyser status changes following the 2024 activity.