Orange Spring Mound

Orange Spring Mound in Yellowstone National Park is one of the most striking and easily recognizable thermal formations in the Mammoth Hot Springs area. Unlike the sprawling, terrace-like structures that dominate much of the landscape, Orange Spring Mound rises dramatically from the ground like a massive, bulbous dome, glowing with shades of orange, white, and cream. This unusual shape and vibrant color make it one of the most photogenic and intriguing geothermal features in the park. While it may look ancient and unchanging, Orange Spring Mound is very much alive — continuously forming, growing, and transforming under the power of Yellowstone’s vast geothermal system.

Orange Spring Mound 

Orange Spring Mound 

Quick Reference: Orange Spring Mound

Attribute	Details
Name	Orange Spring Mound
Location	Upper Terrace Drive, Mammoth Hot Springs, Yellowstone National Park, Wyoming, USA
Type	Travertine Mound / Hot Spring Formation
Geothermal Feature	Active hot spring depositing calcium carbonate
Water Temperature	Typically 140°F–165°F (60°C–74°C)
pH Level	Around 6.2–7.0 (neutral to slightly acidic)
Elevation	Approximately 6,735 feet (2,053 meters)
Formation Process	Hot water rises through limestone, dissolving and depositing travertine on the surface
Colors Origin	Orange, brown, and white tones caused by thermophilic bacteria and mineral flow
Activity Pattern	Continuous and stable, growing slowly over centuries
Nearby Attractions	Canary Spring, Minerva Terrace, Palette Spring, and Liberty Cap
Accessibility	Easily visible from the Upper Terrace Drive; accessible by car
Best Viewing Time	Morning or late afternoon for best light and color contrast
Safety Note	Do not walk on or near the formation; surface is fragile and extremely hot
Fun Fact	The mound continues to grow slowly each year, fueled by mineral-rich water emerging from deep underground

Located along the Upper Terrace Drive in Mammoth Hot Springs, Orange Spring Mound stands out immediately to visitors due to its color and texture. The mound’s brilliant orange hue comes from thermophilic (heat-loving) microorganisms that thrive in the hot, mineral-rich water flowing over its surface. These microscopic life forms produce pigments that reflect different colors depending on the temperature of the water. Where the flow is hottest, the surface tends to appear white or pale; where it’s cooler, bright orange and brown tones emerge, creating a breathtaking gradient of color that seems to glow under sunlight.

The mound itself is primarily made of travertine, a type of limestone deposited by the hot water that seeps up from deep underground. As this water rises through the Earth’s crust, it dissolves calcium carbonate from the surrounding limestone layers. When it reaches the surface and cools, the mineral precipitates out and solidifies, forming the mound’s soft, bulbous layers. Over time, this process builds up the mound inch by inch, giving it its distinctive shape and texture. Though it looks rock-solid, the surface is delicate — soft and wet from constant mineral deposition.

What makes Orange Spring Mound especially fascinating is its slow but continuous growth. Unlike many hot springs in Yellowstone that shift or dry up entirely, this mound has been active for thousands of years, steadily growing taller and broader as new travertine layers form. The hot water seeps from vents at the top and flows gently down the mound’s sides, creating a smooth, almost sculpted appearance. Its formation is not rapid — scientists estimate that travertine deposits grow only a few millimeters each year — but the cumulative effect over centuries is remarkable.

The average water temperature on the mound’s surface is typically between 140°F and 165°F (60°C–74°C), and its chemistry is rich in calcium and carbonate minerals. The combination of temperature, pH balance, and water flow determines where microorganisms can thrive, which in turn shapes the mound’s vivid color patterns. Visitors often notice that parts of the mound are white or gray where water flow is strongest and orange or brown where flow has slowed or cooled. This living interplay between heat, water, and biology makes Orange Spring Mound a dynamic natural sculpture that’s constantly changing in subtle ways.

Orange Spring Mound is one of the easiest geothermal features to visit in the Mammoth Hot Springs region. It’s located directly beside the road on the Upper Terrace Drive, making it accessible for all visitors, including those who may not wish to hike long distances. The site offers an excellent view from designated pullouts, where travelers can safely stop, admire the formation, and take photographs. In the early morning or late afternoon, sunlight enhances the mound’s brilliant orange tones, while cooler weather may bring a faint mist of steam rising from its surface — adding to its ethereal beauty.

Geologists believe that Orange Spring Mound’s unusual dome shape results from a restricted water flow. Unlike wide-spreading terraces where water flows freely across a large surface area, the water here emerges from narrow vents and channels that focus mineral deposits in a smaller space. This limited dispersal causes the travertine to build vertically rather than outward, resulting in the rounded, bulbous form that makes the mound unique among Yellowstone’s hot springs.

Despite its quiet appearance, Orange Spring Mound represents the constant, unseen motion that defines Yellowstone National Park. It stands not just as a beautiful formation but also as a living record of natural history — a monument to water, heat, and time that continues to grow, one mineral layer at a time.