The Roosevelt Arch is a rusticated triumphal arch at the north entrance to Yellowstone National Park in Gardiner, Montana, United States. Constructed under the supervision of the US Army at Fort Yellowstone, its cornerstone was laid down by President Theodore Roosevelt (who just happened to be vacationing in the area. Before this it wasn't planned that he be there.)in 1903. The top of the arch is inscribed with a quote from the Organic Act of 1872, the legislation which created Yellowstone, which reads: "For the Benefit and Enjoyment of the People". The arch is constructed of hexagonal blocks of columnar basalt, quarried locally. The arch is 52 feet high. Two towers or buttresses flank the main archway, pierced by pedestrian passages with heavy wood doors. Yellowstone was the first national park in the world, and local citizens felt that it lacked the grand entrance that such an august place demanded

As one early visitor described the Mammoth Hot Springs, "No human architect ever designed such intricate fountains as these. The water trickles over the edges from one to another, blending them together with the effect of a frozen waterfall." The hot springs were an early commercialized attraction for those seeking relief from ailments in the mineral waters. Today, to preserve these unique and fragile features, soaking in the hot springs is prohibitted. Mammoth Hot Springs are a surface expression of the deep magmatic forces at work in Yellowstone. Although these springs lie outside the Yellowstone Caldera boundary, scientists surmise that the heat from the hot springs comes from the same magmatic system that fuels other Yellowstone hydrothermal areas. A large fault system runs between Norris Geyser Basin and Mammoth, which may allow thermal water to flow between the two. Also, multiple basalt eruptions have occurred in this area. Thus, basalt may be a heat source for the Mammoth area.

Lamar Valley is one of the nation's premier wildlife watching destinations! Elk, bison, deer, and pronghorn thrive in the grasslands of this area, known as the northern range. In fact, some of the largest wild herds of bison and elk in North America are found here. The northern range is critical winter habitat for these large animals, which in turn provide food for several packs of wolves. Coyotes are also common, and occasional bobcat, cougar, or red fox are reported.

he 109-foot (33.2-m) Upper Falls is upstream of the Lower Falls and can be seen from the Brink of the Upper Falls Trail and from Upper Falls Viewpoints. The 308-foot (93.9-m) Lower Falls can be seen from Lookout Point, Red Rock Point, Artist Point, Brink of the Lower Falls Trail, and from various points on the South Rim Trail. The volume of water flowing over the falls can vary from 63,500 gallons (240,374 l)/second at peak runoff in the spring to 5,000 gallons (18,927 l)/second in the autumn.

Watching Old Faithful Geyser erupt is a Yellowstone National Park tradition. People from all over the world have journeyed here to watch this famous geyser. The park’s wildlife and scenery might be as well-known today, but it was the unique thermal features like Old Faithful Geyser that inspired the establishment of Yellowstone as the world’s first national park in 1872. Old Faithful is one of nearly 500 geysers in Yellowstone and one of six that park rangers currently predict. It is uncommon to be able to predict geyser eruptions with regularity and Old Faithful has lived up to its name, only lengthening the time between eruptions by about 30 minutes in the last 30 years. Thermal features change constantly and it is possible Old Faithful may stop erupting someday. Geysers and other thermal features are evidence of ongoing volcanic activity beneath the surface and change is part of this natural system.

The Madison River, a tributary of the Missouri River, begins in Yellowstone National Park at the confluence of the Firehole and Gibbon rivers. This site is called Madison Junction. Both the Firehold and Gibbon rivers are thermally influenced by contributions from geothermal features. The Madison River travels 19 miles (31 km) through Yellowstone National Park before crossing the park boundary and flowing into Hebgen Lake towards Ennis, Montana. It continues northwest from there and meets the Jefferson and Gallatin rivers to form the Missouri River. The Madison River is a renowned recreation destination for fishing, birding, and wildlife viewing. There is a park legend which tells of explorers camping here in 1870 and deciding Yellowstone should be set aside as a national park. It is a wonderful story, but it isn’t true. Explorers did camp at the junction in 1870, but they apparently did not discuss the national park idea.

Grand Prismatic Spring, Yellowstone’s largest hot spring, is 200-330 feet in diameter and more than 121 feet deep. Hot springs are the most common hydrothermal features in Yellowstone. Their plumbing has no constrictions. Superheated water cools as it reaches the surface, sinks, and is replaced by hotter water from below. This circulation prevents water from reaching the temperature needed to set off an eruption. Hydrothermal features are also habitats in which microscopic organisms survive and thrive. They are called thermophiles: "thermo" for heat and "phile" for lover. Although they are too small to be seen with the naked eye, trillions are grouped together and appear as masses of color. They are nourished by energy and chemical building blocks. Colorless and yellow thermophiles grow in the hottest water. Orange, brown, and green thermophiles grow in cooler waters.

Gibbon Falls drops 84 feet (25.6 m) over a remnant of the Yellowstone caldera rim. The caldera was created by a massive volcanic eruption approximately 631,000 years ago. The flow at the falls varies greatly throughout the year. During the spring snow-melt the Gibbon River caries much more water than it will later in the summer, and this season provides the most impressive views of the fallw, but because of weather and all the other variables this falls is always worth a look.