OFFICIAL TRAVEL GUIDE Geology of the Gem State Learn how geological events shaped Idaho’s natural beauty 30 | O! cial Idaho Travel Guide | visitidaho.org 30-35 Geology of the Gem State.indd 30 11/17/20 1:16 PM DEREK BUTLER BY MARISSA LOVELL daho is home to some of the most spectacular As the land engulfed the seafl oor, pieces of rock GREEN geological sites and landscapes in the country. melted into magma and ascended toward the surface. BAY INLET, LAKE PEND These are places that are near and dear to many— The semi-liquid rock cooled gradually as it moved I OREILLE, places where residents and visitors have found peace upward, forming a mammoth mass of granite known NEAR and solace among rugged peaks and rolling hills. It as the Idaho Batholith. Covering about $%,### square SANDPOINT may come as a surprise then, that many of these geo- kilometers of central Idaho, erosion has exposed the logical marvels began in u! er chaos. enormous Idaho Batholith, which can be clearly seen The sharp, sky-piercing peaks of the Sawtooths. in places like the Sawtooth and Bi! erroot ranges. The inky, jagged lava fi eld covering Craters of the Around &#-%# million years ago hot magma broke Moon. The gleaming walls of limestone in the Boul- the surface, creating the Challis volcanic fi eld. Then, der-White Cloud Mountains. How did these won- closer to '% million years ago, things really began drous places come to be? to heat up as the Yellowstone hotspot formed near The simple answer is heat and pressure, but that Idaho’s southwest corner. As the hotspot scorched, doesn’t even begin to tell the magnifi cent geologic rising magma melted sections of the batholith stand- tale of Idaho. ing in its path. Eventually, melted pools of rhyolitic Some "## million years ago, the land that is now magma burst through the earth’s crust in a series of Idaho bordered the Pacifi c Ocean. Rising up from the supervolcanoes, leaving gigantic calderas in its wake. sea, a microcontinent slammed into its coastline— These massive depressions run southwest to north- scraping down its western edge and squeezing the east across southern Idaho toward the site of current oceanic seafl oor in between—ultimately beginning the activity in Yellowstone, forming what we know as subduction of Pacifi c seafl oor beneath the more buoy- the Snake River Basin. It’s important to note that the ant continental North American Plate. Yellowstone hotspot is not moving eastward, as it visitidaho.org | O! cial Idaho Travel Guide | 31 30-35 Geology of the Gem State.indd 31 11/17/20 1:17 PM may appear, but the continental plate is northern Utah and Nevada and was also actually moving above the hotspot. reaching capacity. The lake fi nally burst As the continent passed over the through Red Rock Pass and overfl owed hotspot, the Western Snake River Basin over southeastern Idaho. Water surged was concurrently stretched, forming a deep through the Snake River Canyon on its basin that became known as Lake Idaho. way to the Pacifi c Ocean, carving the can- The giant body of water is assumed to have yon and leaving interesting debris in its been about !,"## feet deep and roughly the wake, such as the “melon gravel” boulder size of Lake Ontario. Lake Idaho covered fi elds near Hagerman. The powerful fl ood much of present-day’s Treasure Valley area is responsible for sculpting some of the re- and drained through Hells Canyon about gion’s most renowned features, including !$ to $ million years ago. Shoshone Falls near Twin Falls and the Idaho chilled out during the next se- Great Salt Lake in Utah. Geology of the Gem State ries of geological events, which occurred Perhaps what makes Idaho even more about !",### years ago. Out of the north, geologically intriguing is the fact that its glaciers came crawling over the state’s history is still being wri% en. The young- mountains. At the northernmost edge of est fl ows at Craters of the Moon National Idaho’s panhandle, a glacial chunk fl owed Monument and Preserve are only about down the Purcell Trench and jammed. $,### years old, and geologists predict The massive ice dam was located where further activity in the region over the the Clark Fork River presently enters next !,### years. Idaho’s mountains are Lake Pend Oreille, impounding what was still moving, as indicated by the recent once the huge glacial Lake Missoula. The earthquakes near Borah Peak in !&'( and lake fi lled beyond its capacity on more Stanley in $#$#. than one occasion, each time sending a Understanding the catastrophic events deluge of water racing across northern that carved Idaho’s dazzling landscapes Idaho and eastern Washington. and the years of nature at play is surely Meanwhile, in southern Idaho, the an- enough to make you fall even more in cient Lake Bonneville covered much of love with the great Gem State. SHOSHONE FALLS These mighty waterfalls stand 212-feet high, about 45 feet higher than Niagara Falls, with water spilling over a nearly 1,000-foot-wide rim. When the Lake Bonneville fl ood unleashed its waters nearly 15,000 years ago, the massive fl ow tore through the area, sculpting the walls of the Snake River Canyon and ripping away the can- yon fl oor to form impressive features such as Shoshone Falls. Its powerful cascade is a constant reminder of the forces that came before it, which shaped the scenery as far as the eye can see. 32 | O! cial Idaho Travel Guide | visitidaho.org 30-35 Geology of the Gem State.indd 32 11/17/20 1:16 PM VISIT IDAHO BRUNEAU DUNES STATE PARK Standing tall and proud in the southwest Idaho desert, Bruneau Dunes State Park is home to the tallest single-structured sand dune in North America. Geologists believe that prevailing winds carried sand from the Bonneville fl ood and deposited it where the dunes stand today outside of Mountain Home. Bruneau Dunes still re- mains at the mercy of the winds. CRATERS OF THE MOON NATIONAL MONUMENT AND PRESERVE CITY OF ROCKS NATIONAL RESERVE The lava fl ows at Craters of the Moon Na- tional Monument and Preserve didn’t hap- The rocks here were formed by a volcanic eruption pen that long ago, geologically speaking. some 34 million years ago; then erosion worked the bedrock, sculpting the citylike features for which Lava erupted from the deep cracks of the the area is named. Emigrants of the California Trail Great Ri! between "#,$$$ and %,$$$ years vividly described passing through a “Silent City of ago, sending lava oozing onto &"' square Rocks”—an otherworldly landscape where tall stone miles before coming to rest. Today, visitors spires sprung from the earth and narrow canyons can explore the cavernous lava tubes and snaked through the sagebrush-fl anked desert. sleepy cinder cones, as geologists believe this area is lying dormant for now. VISIT IDAHO VISIT IDAHO BRUNEAU DUNES STATE PARK VISIT IDAHO CRATERS OF THE MOON NATIONAL MONUMENT AND PRESERVE visitidaho.org | O! cial Idaho Travel Guide | 33 30-35 Geology of the Gem State.indd 33 11/17/20 1:17 PM MESA FALLS Over the past 2.1 million years, the Yellowstone region has produced three large volcanic eruptions, one of which re- sulted in the creation of Mesa Geology of the Gem State Falls. This particular eruption occurred 1.3 million years ago, forming a large, basin-shaped volcanic crater known as the Henry’s Fork Caldera. As this caldera deepened, a ledge SCAN THE CODE for formed over which the Snake a guide to River began to fl ow, resulting Northern in the impressive waterfall Idaho’s that we see today. stunning waterfalls. VISIT IDAHO SAWTOOTH MOUNTAINS Glaciers tore through the land as they Named for their distinct jagged peaks, invaded Idaho from the north, creating the Sawtooth Mountains are one of the rock dust that se" led in Lake Missoula. best illustrations of the Idaho Batholith. Floods spilled out over the land and even- As the magma ascended, sections shi! ed tually dried up. Prevailing winds carried into one another, creating the towering silt and dust where it se" led on the land, craggy mountains of solid granite that creating the rolling hills that we now call we see today. A section at the northern the Palouse. The loess soil—a very fi ne, end of the Sawtooth Range exudes a pink light soil—here is exceptional for farm- hue rather than the usual sparkling gray, ing, as the abundance of silt particles ensures good irrigation, drainage and soil PALOUSE PRAIRIE indicating a section of batholith that is a VISIT IDAHO bit younger than the rest of the massive aeration. range. Glaciers also ravaged the moun- ancient Lake Missoula—is located where tains, leaving behind U-shaped valleys LAKE PEND OREILLE the Clark Fork River enters the lake today. and pristine lakes like Redfi sh Lake. Known for its depth and outstanding Glacial activity carved out the #,#$%-foot beauty, Lake Pend Oreille in northern lake, making it the fi ! h-deepest lake in PALOUSE PRAIRIE Idaho is evidence of the ancient glacial the nation. Similar to the formation of the Bruneau lake from which it formed. It’s believed Dunes, water and wind created the fertile that the massive ice dam—which spurred Palouse region in north-central Idaho. MICHAEL BONOCORE SAWTOOTH MOUNTAINS, STANLEY 34 | O! cial Idaho Travel Guide | visitidaho.org 30-35 Geology of the Gem State.indd 34 11/17/20 1:17 PM.