English: Hot springs are sites where groundwater emerges at the Earth’s surface (or on the seafloor). Hot spring water has to be higher in temperature than the human body (an admittedly arbitrary definition): over 98° Fahrenheit or over 37° Celsius. Geysers are hot springs that episodically erupt columns of water. The highest concentration of geysers and hot springs anywhere is the Yellowstone Hotspot Volcano in northwestern Wyoming, USA.

Orange Spring Mound is located in the far-western part of Mammoth Hot Springs, a large complex of travertine terraces formed by calcium carbonate precipitation from hot spring water. Mammoth Hot Springs is on the northern periphery of the Yellowstone Hotspot Volcano and occurs well outside the 640,000 year old caldera boundary. Most hydrothermal features at Yellowstone deposit geyserite (siliceous sinter), an opaline chemical sedimentary rock. Opal and geyserite form where hot spring water is rich in dissolved silica, derived from leaching of subsurface Quaternary-aged rhyolitic volcanic rocks. In the Mammoth Hot Springs area, subsurface hydrothermal water is rich in dissolved calcium carbonate, derived from leaching of Mississippian-aged Madison Group limestones. Upon emerging at the surface, hot spring water precipitates CaCO3, resulting in travertine deposits.

The orangish-brown coloration at Orange Spring Mound is from the presence of microbes (bacteria) that thrive in the hot water.