Gator Girl Rocks

Rockhounding Idaho

Idaho is an extraordinary state for rockhounding.  Idaho's nickname is 'The Gem State.'  Originally suggested as the name for the land that became the State of Colorado, the name "Idaho" was used for a steamship that traveled the Columbia River.  With the discovery of gold on the Clearwater River in 1860, the diggings began to be called the Idaho mines.  "Idaho" is a coined or invented word, and is not a derivation of an Indian phrase "E Dah Hoe (How)" supposedly meaning "gem of the mountains."  Idaho’s mountains have rich veins of silver (and other metals such as gold, lead, and zinc).  In addition to the state’s rich mineral ore legacy, Idaho also has garnets, opal, agates, jasper, quartz, petrified wood, and a wide variety of fossils.  The state also is home to an incredible variety of geological formations including immense lava flows and Hell’s Canyon, the deepest canyon in the U.S.  In addition, five meteorites are known to have been found in Idaho.

State Rocks, Gemstones, Minerals, Fossils, & Dinosaurs

Rockhounding Tip:  Knowing state rocks, gemstones, minerals, fossils, and dinosaurs often can be very useful information for rockhounders.  Ordinarily, states with significant mineral deposits, valuable gemstones, fossils, or unusual or significant rock occurrences will designate an official state mineral, rock/stone, gemstone, fossil, or dinosaur to promote interest in the state’s natural resources, history, tourism, etc.  Accordingly, such state symbols often are a valuable clue as to potential worthwhile rockhounding opportunities.

State Gemstone:  Star Garnet (1967)

Idaho designated the star garnet as its official state gemstone in 1967.  Star garnet is an unusual form of garnet.  Asterism, or the star effect, is associated mostly with sapphire and star ruby.  But, fact a small of group of other gemstones also can exhibit this effect though specimens are fairly rare.  The other star gems include:  chrysoberyl, citrine, diopside, emerald, moonstone, quartz, & spinel.  Star garnets are so rare that thus far they have only been found in two places in the world: in the state of Idaho and in India.  The 12-sided (dodecahedron) crystals found in Idaho range in size from sand particles to golf-ball or larger size.  The garnet varieties that occasionally exhibit asterism are almandine and a mixture of almandine and pyrope garnet.  Star garnets usually are opaque and colored a deep brownish red or a reddish black.  Like all star gems, the star effect is caused by inclusions of rutile.  But in order to display the star effect the rutile needles must have the right alignment to reflect light in a pattern forming a multi-ray star.  Most Idaho star garnets display a 4-ray star, but 6-ray stars are sometimes seen.

State Fossil:  Hagerman Horse Fossil (1988)

Idaho designated the Hagerman Horse Fossil as its official state fossil in 1988.  Discovered in 1928, the Hagerman Horse originally was described as Plesippus shoshonensis.  Subsequent research found the Hagerman horse to be the same as a previously described species discovered in Texas and named by paleontologist Edward Drinker Cope as Equus simplicidens.  The Hagerman horse is the oldest known representative of the modern horse genus Equus (includes horses, donkeys, and zebras) and is believed to be more closely related to the living Grevy's zebra in Africa.  The 3.5 million year old sediments at the Hagerman Fossil Beds National Monument contain the world's richest known fossil deposits from the late Pliocene epoch.  They have yielded about two hundred horse skeletons, twenty of which are complete.  The more than 200 vertebrate, invertebrate, and plant species preserved there represent the last vestiges of animals that existed prior to the Ice Age and the earliest appearances of modern flora and fauna.

Rockhounding Resources

Idaho Geological Survey

 

• Lanny R. Ream, Idaho Minerals: The Complete Reference and Guide to The Minerals of Idaho (2d ed. 2004). 
• Lanny R. Ream, The Gem & Mineral Collector's Guide to Idaho (Rev. ed. 2000).
• John A. Beckwith, Gem Minerals of Idaho (Rev. ed. 1972)
• David D. Alt & Donald W. Hyndman, Roadside Geology of Idaho (1993).
• H.C. Dake, Northwest Gem Trails (3d ed. 1962 - originally published in 1950).
• Garret Romaine, Rockhounding Idaho (2010).
• Allan W. Eckert, Earth Treasures Vol. 3 - Northwestern Quadrant (1986; reprint in 2000). 
• James Martin Monaco & Jeannette Hathway Monaco, Fee Mining & Rockhounding Adventures in the West (2d ed. 2007). 
• Kathy J. Rygle & Stephen F. Pedersen, Northwest Treasure Hunter's Gem & Mineral Guide (4th ed. 2008).

Museums of Interest to Rockhounders

Idaho Museum of Natural History
Idaho State University – Pocatello, Idaho
The museum exhibits Idaho rocks, minerals, gemstones, and fossils.  In addition, the museum’s ‘Trackways of Idaho’ exhibits 200 million year old tracks from spiders, dinosaurs, and early mammals preserved in southern Idaho sandstone.  The museum’s exhibits also include ice-age megafauna fossils.  The Pleistocene fossils include saber-tooth cats, giant bison, and the Hagerman horse.

 

Idaho Museum of Mining & Geology
Boise, Idaho
The museum exhibits rocks, minerals, gemstones, fossils, and artifacts.

 

Wallace District Mining Museum
Wallace, Idaho
Wallace, Idaho is famous as the Silver Capital of the World.  Over a billion ounces of silver has been extracted from the rich mines in this mineral rich area (the mines also produce gold, lead, and zinc).  My great grandmother was married in Wallace, Idaho … so, you know I had to stop and see the town, the mining museum … and eat an ice cream cone with dad.

 

Orma J. Smith Museum of Natural History
The College of Idaho – Caldwell, Idaho
The museum, located in Boone Hall, exhibits rocks, minerals, and fossils.  The college also exhibits the Glen L. and Ruth M. Evans Gem and Mineral Collection that includes approximately 2,000 cabochons.

 

Shoshone County Mining & Smelting Museum
Kellogg, Idaho
In addition to extensive displays regarding the Bunker Hill Mining District, the museum exhibits local minerals as well as minerals from around the world.

 

Places to Visit - Interesting Sites To See

Hagerman Fossil Beds National Monument
Hagerman, Idaho
The Hagerman Fossil Beds National Monument is home to the largest concentration of Hagerman Horse (Equus simplicidens) fossils in North America, including thirty complete horse fossils and portions of two hundred individual horses.
  This internationally significant Monument protects the world's richest late Pliocene epoch (4 - 3 million years ago) fossil deposits:  over 220 species of plants and animals!

 

Craters of the Moon National Monument & Preserve
South Central Idaho near Arco, Idaho
The Craters of the Moon National Monument & Preserve is a vast ocean of lava flows with scattered islands of cinder cones and sagebrush.  Over the past 15,000 years, lava eruptions created a rugged and unique landscape.  The national monument includes three major lava fields that lie along the Great Rift of Idaho, with some of the best examples of open rift cracks in the world, including the deepest known on Earth at 800 feet.  There are excellent examples of almost every variety of basaltic lava as well as tree molds (cavities left by lava-incinerated trees), lava tubes (a type of cave), and many other volcanic features.  I visited there in 2009.

 

City of Rocks National Reserve
Almo, Idaho
City of Rocks National Reserve & State Park is located in south central Idaho just north of the state border with Utah.  City of Rocks and the adjacent Castle Rock State Park are composed largely of Oligocene granitic rock.  The unusual landforms are the result of weathering, mass wasting, and erosion on the granitic rocks of the Almo Pluton and Green Creek Complex.  Prior to the Civil War, this unique geologic area became a landmark for wagon trains on the California Trail.  A few granite pinnacles and monoliths are over sixty stories tall and over 2.5 billion years old.

 

Minnetonka Cave
Bear Lake County, Idaho
Minnetonka Cave, located in the Caribou-Targhee National Forest at the north end of Bear Lake in southeaster Idaho, is the largest limestone cave in Idaho.  The cave features stalactites and stalagmites.  Numerous fossils of animals that lived in the tropical waters of the Mississippian Period are found in the cave walls and ceiling.  These fossils include:  horned coral, honeycombed coral, brachiopods, bryozoans, and crinoid stems. 

 

 

Rockhounding Sites for Children & Families

Star Garnets
Emerald Creek Garnet Area - Near Clarkia, Idaho
The Forest Service has developed the Emerald Creek Garnet Area as a place where the public may collect star garnets.  In the past, people would dig in the stream bed in search of the garnets.  Now, due to concerns for water quality, aquatic habitat, and public safety, the Forest Service provides a stockpile of garnet bearing gravels from which people can gather material to run through one of two sluice boxes in search of garnets.  The site is open during the summer.

 

Opals
Spencer Opal Mines – Spencer, Idaho
Commercial (fee access) business.  The opal mine site, located in northwestern Idaho west of Yellowstone National Park, occurs in a rhyolite and obsidian flow full of gas pockets.  The opal solution or silica was a secondary deposit carried by geyser activity.  The opal was hydrothermally deposited inside hollow geodes in successive layers.