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Three Forks in Gallatin County, Montana — The American West (Mountains)
 

Thunder Horses

 
 
Thunder Horses Marker image. Click for full size.
Photographed by Barry Swackhamer, July 27, 2025
1. Thunder Horses Marker
Inscription. From 38 to 30 million years ago, great herds of rhinoceros-like herbivores, called Megacerops, roamed this part of Montana. Megacerops, also known as Brontotheres, were massive animals. Classified as Perissodactyla, Megacerops had three toes on its front feet and four toes on its back feet. Adults stood 8 feet tall at the shoulder and were around 16 feet in length; they weighed as much as two tons. They were about as big as African Forest Elephants are today. Megacerops had a branched horn on its snout. The snout may have functioned for mating purposes and as defense against the predators of the time. The climate at that time was warm and damp with lakes surrounded by reeds and other riparian vegetation.
Megacerops went extinct about 30 million years ago. Scientists have speculated that climate change and the resulting change in vegetation may have caused their extinction. The animal's primitive teeth may not have been able to browse the leaves and fruit it lived on, contributing to its disappearance.
The Lakota Indians found Megacerops fossils uncovered by rainstorms on the Great Plains. Many believed the animal caused
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thunderstorms when running over the clouds and called them Thunder Horses.

Shedd's Bridges
Many settlers who came to Montana in the 1860s quickly saw opportunity and were quick to recognize the needs of travelers in the territory. As immigrants from Scotland, James Shedd came to Montana Territory about 1864 and built bridges across the Madison and Jefferson rivers a mile or so north of Three Forks. He and his wife, Elizabeth, charged travelers tolls paid in gold dust, to cross the structures. Shedd built a hotel, called Bridge House, to serve sojourners on the roads between the Gallatin Valley and Virginia City and Helena. By 1871, the Shedds operated seven toll bridges in the area. A small settlement called Bridgeville, grew up around their hotel. Shedd sold the operation in 1880 and the hotel burned down in 1881.

Geo-facts:
• Megacerops means "giant horned face" in Greek
• Because of its great size, Megacerops had few predators, except for carnivorous mammals called creodonts and nimravids.
• The order Perissodactyla also included horses, rhinos, and tapirs.
Geo-activity;
• Imagine the fields on both sides of the highway filled with bellowing herds of Megacerops rather than cattle or horses. What do you think the area looks like then?

 
Erected by Montana
Thunder Horses Marker image. Click for full size.
Photographed by Barry Swackhamer, July 27, 2025
2. Thunder Horses Marker
Department of Transportation.
 
Topics. This historical marker is listed in this topic list: Paleontology. A significant historical year for this entry is 1864.
 
Location. 45° 55.529′ N, 111° 35.974′ W. Marker is in Three Forks, Montana, in Gallatin County. It is on U.S. 287 near Interstate 90, on the left when traveling north. The marker is located at the Three Forks Rest Area/. Touch for map. Marker is at or near this postal address: 10778 U.S Highway 287, Three Forks MT 59752, United States of America. Touch for directions.

Regionally, this marker is in Yellowstone Country and in Greater Bozeman. It is also in the American Mountain West and in the Lewis & Clark Corridor. Globally, it is in North America, the Rocky Mountains, the Western Hemisphere, the Western World, and the Anglosphere. Historically, it finds itself in what was once Rupert’s Land and also the Louisiana Purchase.

Other nearby markers. At least 8 other markers are within 3 miles of this marker, measured as the crow flies: Three Forks Post / John Colter (here, next to this marker); The Gallatin Valley / Gallatin City (a few steps from this marker); A Trail Through History / When Montana's Roads Had Names
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(within shouting distance of this marker); George Drouillard (1773-1810) (approx. 2 miles away); Colter’s Run (approx. 3.1 miles away); Native Americans (approx. 3.1 miles away); European Interest in the Missouri (approx. 3.1 miles away); Fur Trade (approx. 3.1 miles away). Touch for a list and map of all markers in Three Forks.
 
 
Credits. This page was last revised on August 24, 2025. It was originally submitted on August 24, 2025, by Barry Swackhamer of Brentwood, California. This page has been viewed 82 times since then and 15 times this year. Photos:   1, 2. submitted on August 24, 2025, by Barry Swackhamer of Brentwood, California.
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Jul. 25, 2026