West Thumb Geyser Basin is one of the smallest geyser basins in Yellowstone yet its location along the shore of Yellow-stone Lake ranks it as the most scenic. West Thumb derived its name from the thumb-like projection of Yellowstone Lake and the name was given by the 1870 Washburn Expedition. It was also known as Hot Spring Camp. West Thumb has less geyser activity than other basins. But West Thumb, for its size, has it all-hot springs, pools, mud pots, fumaroles and lake shore geysers.

Fishing Cone has been the most popular feature. Its unusual location along the lake shore and its symmetrical cone were popularized by early stories of "boiled trout." Abyss Pool is also noted for its depth and colors.

The Thumb Paint Pots are constantly changing. In the 1920s and 30s they were very extensive and active. Now they are less active but, depending on moisture, they still build mud cones.

Since the mid 1970s, West Thumb has decreased in thermal activity. Some temperatures have cooled in the basin allowing large colonies of algae and cyanobacteria to grow. As a result, large newly-formed microbial mats flourish on the run-off channels and along the edges of pools.

OCCASIONAL GEYSER
Temperature 200-206°F Interval 20-40 minutes. Duration 4-5 minutes. Height 3-12 feet. This lake shore geyser was named by C.Max Bauer, author of The Story of Yellowstone Geysers, in 1935. It is located a half mile north of the main features of West Thumb. The geyser is situated in pre-glacial geyserite, estimated at nearly 18 feet thick. This indicates it is a very old feature and was more active in the past, probably as a hot spring, than it is today. Occasional erupts from three vents. The main, round vent stands above the others and splashes water 3 to 12 feet high during an eruption, while the other two vents generally are restricted to boiling and churning. The run-off plunges over an overhang, undercut by wave action, into Yellowstone Lake.

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TWIN GEYSERS
Temperature 201 °F Interval irregular to dormancy. Duration 3-4 minutes. HeightGO-120 feet. Twin Geysers are actually two vents together which have the nickname of Maggie and Jiggs, taken from early 20th century cartoon characters. The geysers have had periods of long dormancy. A 1934 violent eruption reached 120 feet and ejected water, mud and sticks. When Twin Geysers are active, eruptions can occur every four to eight hours until they become dormant again. Even during dormant periods the geysers constantly bubble and boil, discharging an even flow of water. Temperatures of 213° to 218° have been recorded during hot periods. Iron oxides have stained the area around the vent.

ABYSS POOL
Temperature 172°F Dimensions 30x57 feet. Depth 53 feet. Abyss Pool is a colorful and interesting pool in the West Thumb Geyser Basin. Abyss is the deepest pool known in Yellowstone and received its name for its abyss-like depth. The dark green-colored water gives the illusion of a bottomless pool. Vandalism may have changed this pool's temperature. Coins and other debris thrown in have caused the vent to plug. The reduced spring flow also reduced the pool temperature, allowing abundant algae growth along the edge and run-off channels. The extensive microbial mats now support ephydrid flies, spiders and killdeers. An unusual eruption in 1987 caused the pool to surge and temporarily destroyed the microbial mats.

BLACK POOL
Temperature 132°F Dimensions 40x75 feet. Depth 30 feet. Black Pool is one of the largest springs in the West Thumb Geyser Basin. The dark-colored water is the combination of the natural, transparent blue of the water and the orange algae lining of the pool. The low temperature of the pool is responsible for the abundant growth of the orange-colored microbial mats. Algae and cyanobacteria in combination with sinter deposits have created coral-like formations on the sides of the pool but these are visible for only a few feet. The pH of Black Pool is a slightly alkaline 7.8.

FISHING CONE
Temperature 170.4°F Interval dormant. Duration minutes to hours. Height 3 feet. Fishing Cone is a thermal feature unique to Yellowstone. It is situated on the shore of Yellowstone Lake and received its name from early explorers who stood on the cone and cast their lines into the lake to catch fish. Without taking the fish off the hook they parboiled them in the vent of Fishing Cone. However, the shoreline has changed since those times; Fishing Cone is usually inundated by high water during the early summer. It erupted once during the 1920s and '30s but the cold water of the lake has altered its eruptive behavior.

LAKE SHORE GEYSER
Temperature 198.6°F Interval 30-60 minutes-dormancy. Duration 10 minutes. Height 20-30 feet. Lake Shore Geyser is very similar to Fishing Cone. It is also on the shore of Yellowstone Lake, but its vent is usually covered by water. By August or September the water level is usually low enough to expose the crater. Lake Shore Geyser has long periods of dormancy and geyser predictions are difficult. When it does erupt, a column of water reaches 20-30 feet high which gradually decreases in force after ten minutes.

BLUE FUNNEL SPRING
Temperature 172-182°F Dimensions 18 feet diameter. Blue Funnel Spring is a small, blue concentric pool located in the center of West Thumb Geyser Basin. When one walks past this spring, its vent appears to move and reposition. This phenomenon is not unique to Yellowstone's thermal features, but it is easily observed in Blue Funnel Spring. It is an optical illusion caused by refraction. It results when light traveling through the air strikes the surface of water at an oblique angle. One side of the wave front enters the water before the other and is retarded-since light travels more slowly in water than in air-while the other side continues to move at its original speed until it too reaches the water surface. As a result, the light ray bends in the denser water and is refracted, giving the illusion that an object has a different location than it actually has.

SURGING SPRING
Temperature 193°F Dimensions 33x62 feet. Depth 28 feet. Surging Spring received its name from the occasional surges of water which overflow from the spring. The cyclic activity which occurs nearly every four to five minutes, begins with ebullition and boiling a foot high. The water level of the spring rises and overflows for approximately two minutes. After a surge, the water level drops four inches below the discharge channel. The overflow from Collapsing Pool may occasionally upset this cyclic balance. An estimated 1200 gallons per minute discharges during an overflow of Surging Spring.

WEST THUMB PAINT POTS
Temperature 187-199.8 Dimensions 30 feet diameter. These mud pots were originally named Mud Puffs by the 1878 Hayden Survey. The Paint Pots were one of the highlights for early tourists. They ventured to West Thumb by stagecoach from the Upper Geyser Basin and explored West Thumb's thermal features. From there they continued their journey by boat across Yellowstone Lake to Lake Hotel. Since the discovery of West Thumb Geyser Basin, the Paint Pots have been an active and fascinating feature of the basin. They were very similar to the Fountain Paint Pots, and they were known for the large mud cones produced by midsummer as the mud thickened. The paint pots began changing during the 1970s as roads and buildings were removed adjacent to the paint pots. Ground water now floods and inundates the pots, producing a soupy, bubbly, frothy spring.