About Lost Rivers Valley

The Big Lost River

The Big Lost River is a major river in the U.S. state of Idaho, about 135 miles (217 km) long.[4] It starts in the Rocky Mountains and flows in a generally southeast direction into the Snake River Plain. True to its name, the Big Lost River’s surface flow does not reach any larger river, but vanishes into the Snake River Aquifer at the Big Lost River Sinks, giving the river its name.[2] The river is one of the Lost streams of Idaho, several streams that flow into the plain and disappear into the ground.

It rises at the confluence of the North Fork and East Fork Big Lost River deep in the Pioneer Mountains, a subrange of the Rockies, in Custer County, south-central Idaho. It flows northeast then turns sharply southeast at the confluence with Thousand Springs Creek which comes in from the left and into Butte County. The river is dammed to form Mackay Reservoir near the town of Mackay, then continues south through an agricultural valley, passing Arco. After Arco the river begins flowing east, then northeast, and finally due north. The river terminates at the Big Lost River Sinks, a patch of marshland where its water drains into the ground.

Despite the fact that its surface flow is lost (hence its name) a short distance out of the mountains, the river is hydrologically connected to the Snake River, the largest river of Idaho by discharge, via the Snake River Aquifer and various springs along the course of the Snake in its journey through the plain.

  1. “Big Lost River”. Geographic Names Information System. United States Geological Survey. 1979-06-21. Retrieved 2010-11-21.
  2. ^ Jump up to:a b “Subbasin Assessment – Watershed Characterization” (PDF). Big Lost River Subbasin Assessment and TMDL. Idaho Department of Environmental Quality. 2004-05-06. Archived (PDF) from the original on 22 November 2010. Retrieved 2010-11-21.
  3. Jump up^ “USGS Gage #13132500 on the Big Lost River near Arco, ID” (PDF). National Water Information System. U.S. Geological Survey. 1946-present. Retrieved 2010-11-21. Check date values in: |date= (help)
  4. Jump up^ U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National Map, accessed May 4, 2011

The Little Lost River

The Little Lost River is a river in the central part of the U.S. state of Idaho. The river is about 49 miles (79 km) long[3] and drains an arid farming valley, the Little Lost River Valley, bordered by the Lost River Range on the west and Lemhi Range on the east. Instead of emptying into a larger body of water, it disappears into the ground at the edge of the Snake River Plain, a phenomenon that gives it its name. The water feeds into the Snake River Aquifer, eventually reaching the Snake River through a series of springs farther west.

It rises at the confluence of two similarly sized streams, Summit Creek and Sawmill Creek, 10 miles (16 km) north of Hawley Mountain, in the middle of the Little Lost River Valley. The river flows generally south-southeast receiving many tributaries such as Wet (the largest), Badger, Deer, Uncle Ike, Sands, Cedarville, South, and Hurst creeks. Along its course the Little Lost is used for irrigation, but the only settlement of any size is Howe, situated near the mouth. A few miles past Howe, the river disappears into the earth at about 4,806 feet (1,465 m) above sea level.

The river drains about 963 square miles (2,490 km2) of land entirely in Butte County. Its valley is about 50 miles (80 km) long and 20 miles (32 km) wide, with a floor width of 7 miles (11 km). Precipitation is generally very low and mostly in the form of snow.

  1. “Surface Water: Little Lost River Subbasin Assessment and Total Maximum Daily Loads”. Idaho Department of Environmental Quality. Retrieved 2010-11-21.
  2. Jump up^ “USGS Gage #13118700 on the Big Lost River below Wet Creek, near Howe, ID” (PDF). National Water Information System. U.S. Geological Survey. 1958-present. Retrieved 2010-11-21. Check date values in: |date= (help)
  3. Jump up^ U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National Map, accessed May 4, 2011

The Lost River Range is a high mountain range of the Rocky Mountains, located in central Idaho, in the northwestern United States.[1]

It runs southeast for approximately 75 miles (121 km) from the Salmon River near the community of Challis to the Snake River Valley near Arco. To the west are the valleys of the Salmon and the Big Lost Rivers, while to the east are the Little Lost River and Pashimeroi Valleys.

The range starts at the east bank of the Salmon River, at an elevation of about 5,000 feet (1,500 m). It quickly rises to Grouse Creek Mountain (11,085 ft, 3378 m) and Dickey Peak (11,141 ft, 3395 m), and then descends to Double Springs Pass, location of one of just two roads to cross the range. Nearby is an interpretive site explaining the effects of the magnitude 6.9 Borah Peak earthquake that hit the range on October 28, 1983. The Big Lost River Valley fell and the Lost River Range rose, leaving a fault scarp of up to 14 ft (4.3 m) along the base of the mountains.

Borah Peak, Idaho, looking east (note 1983 earthquake fault).

The range then rises into its high central section, which includes many of the state’s highest peaks. Borah Peak, the highest, climbs to 12,662 ft (3,859 m). Further south are Mount Idaho (12,065 ft, 3677 m), Leatherman Peak (12,228 ft, 3727 m), Mount Church (over 12,200 ft, 3720 m), Mount Breitenbach (12,140 ft, 3700 m), and Lost River Mountain (12,078 ft, 3681 m). To the east of this section of the range lie the remote canyons of the Upper Pashimeroi Valley, including scenic Merriam Lake.

Panorama of the Upper Pashimeroi Valley, including Leatherman Peak (center)

The range then descends to Pass Creek Summit, the second road to cross its crest. It continues to King Mountain (10,612 ft, 3235 m), a favorite site for hang gliders. Finally it descends sharply to the Snake River Valley near the community of Arco, at an elevation of 5,300 ft (1,600 m).

Merriam Lake, Idaho, in the Lost River Range.

  1. “Lost River Range”. Geographic Names Information System. United States Geological Survey. Retrieved October 13, 2012.
  2. “Lost River Range”. PeakBagger. Retrieved October 13, 2012.
 Sourced from Wikipedia


A gymnasium of basalt in Arco, Idaho

Building Image
      One of the least likely structures to be built of stone is a gymnasium, but the building above is the Recreation Hall (and sometime city offices) of Arco, Idaho. The Rec Hall was built as a WPA project in 1937 and 1938, and renovations including a new roof in the 1990s allow basketball and other activities to continue in the Rec Hall today.      Another unusual feature of this building is that the stone is vesicular basalt. Basalt, or “lava-rock”, is a dark volcanic rock formed when mafic magmas reach the earth surface and flow across the landscape. Magma, or molten mineral material, contains gases that usually escape to the atmosphere. However, sometimes the gases haven’t time to escape and form bubbles or vesicles in the rock, making the porous or vesicular texture seen below.

Basalt is a very hard rock, and it presented many challenges for this building. One challenge during the construction process was that the WPA’s masons couldn’t hammer the basalt into regular blocks for a tightly fitting wall. Instead, they mortared the irregular stones together and then traced small “seams” in their mortar to give the appearance of tightly fitting stones. A challenge that continues today is that the porous basalt leaks a little water when it rains, so that moisture appears inside the walls. That could be a huge problem, but Arco gets only an average of about 10 inches (25 cm) of precipitation per year, some of it as snow, so the leakiness of this stone isn’t the issue that it might be elsewhere.

Stone Image
Stone Image
The gymnasium or red hall shown above is not unique in Arco – the church shown below is also built of basalt:
Stone Image
      The choice of this less-than-ideal stone for such an unusual building as the Rec Hall has everything to do with Arco’s location. Arco sits at the edge of the Snake River Plain, which is covered with basalt flows that flooded the landscape (in fact, they’re called “flood basalts”). The image just below shows Arco in the foreground and black expanses of flood basalt in the distance to the west (in the direction of Craters of the Moon National Monument, twenty miles to the west). Our Rec Hall is the nearest of three red-roofed buildings in a line on Arco’s main street; the church’s red roof is the most distant of the three.
Stone Image
      The final image below shows one of the basalt flows south of Arco. Arco sits at the foot of the mountain in the right background of the image. The outcrop shows the vesicular nature and irregular breakage of the basalt that made it such a challenge for the building above.
Stone Image



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