Rocky Mountain National Park (Part 4)

This U-shaped valley was carved out by the 500-foot-thick Fall River Glacier about 15,000 years ago. After the glacier melted in Horseshoe Park, lateral moraines remained along the path of its recession as well as a terminal moraine at the end of the valley. Sediment from the meltwaters of the glacier formed the meadows.

The Alluvial Fan Trail leads to a bridge over the Roaring River at the site of the Lawn Lake Flood and ends at Horseshoe Falls Overlook.

As the Fall River Glacier receded through this valley and melted in Horseshoe Park, huge ice chunks split from the glacier and were buried in the gravel. The ice chunks created depressions called kettles that became the Sheep Lakes once the ice melted. The lakes are named for the bighorn sheep which are often seen in the area.

Mount Meeker and Longs Peak were previously known as Nesótaieux, or “The Two Guides,” by the Arapaho and Les Deux Oreilles, or "The Two Ears,” by French fur trappers. 

Longs Peak, Storm Peak, Half Mountain, McHenry’s Peak, Thatchtop, Powell Peak, Taylor Peak, Hallett Peak, Flattop Mountain, and Notchtop

Moraine Park is a meadow between two lateral moraines on Bear Lake Road. The Thompson Glacier carved out this valley around 18,000 years ago before eventually melting here. The meltwater consolidated into an ancient glacial lake that silted up and drained over time to form Moraine Park.

Moraine Park Discovery Center contains several exhibits explaining the geological and glacial history of the park. The building was constructed in 1923 as the Assembly Hall of Moraine Park Lodge, a resort owned by Imogene Green MacPherson. The NPS purchased the property in 1931 and removed the other cabins before the Civilian Conservation Corps reworked the lodge into a museum and built the amphitheater in 1934 and 1935. The lodge was listed on the National Register of Historic Places in 1976 and the listing was expanded to include the amphitheater in 2005.

The park has a long geologic history and its oldest rocks are gneiss and schist, metamorphic rocks that formed from great heat and pressure deep beneath the surface of the Earth about 1.7 billion years ago during the Precambrian Era. Around 1.7-1.4 billion years ago, magma intruded into these rocks deep underground and cooled to form igneous rock, primarily granite. Pikes Peak granite formed as molten rock hardened to create the continents about 1 billion-300 million years ago.

Between 500-300 million years ago, throughout much of the Paleozoic Era, a shallow inland sea covering this area deposited layers of limestone and dolomite. Around 300 million years ago, uplift created the Ancestral Rocky Mountains and sediments eroded from the mountains formed the Fountain Formation 296-290 million years ago. Over 150 million years, the mountains uplifted, eroded, and were buried.

The Western Interior Seaway formed about 100 million years ago during the Mesozoic Era and marine deposits became Pierre Shale about 70 million years ago. About 68 million years ago, a mountain building event known as the Laramide orogeny began lifting the Front Range and water carrying sediments to the foot of the mountains deposited the Denver Formation.  The Front Range continued to rise until about 55 million years ago during the Cenozoic Era but then eroded down over time before being buried in sediment deposited from the central Rocky Mountains around 40 million years ago.

About 37 million years ago, a volcanic eruption in the Collegiate Range covered the area in ash, forming 20 feet of rhyolite, which eroded to form the Castle Rock Conglomerate. Another period of uplift around 10 million years ago raised the Front Range to about its current height and erosion along new drainage patterns shaped the mountains.

The start of the Quaternary Ice Age 2.58 million years ago brought several periods of glaciation that carved out U-shaped valleys and cirques. Since glacial deposits often erase indications of older glaciations, only the most recent Bull Lake Glaciation (200,000-130,000 years ago) and Pinedale Glaciation (30,000-10,000 years ago) left behind evidence that can be easily distinguished within the park. Glaciers melted at various locations including Moraine Park, Glacier Basin, Horseshoe Park, and the Kawuneeche Valley.

Sprague Lake Trail loops around the perimeter of Sprague Lake, a 13-acre subalpine lake in Glacier Basin named after Abner and Alberta Sprague. The Spragues moved to Moraine Park in 1875 and operated a resort for hunting, fishing, and dude ranching that they sold to James Stead in 1900. In 1910, the Spragues built a guest lodge by Sprague Lake and dammed Boulder Brook at the far end to enlarge it and improve fishing. The National Park Service (NPS) purchased the property and gave the Spragues a 20-year lease before tearing down the structures in 1957. In 1962, the NPS acquired Stead’s Ranch and Hotel, removed the buildings, and allowed the area to naturally revegetate.