• Ancient Seafloor: The Bloomington Formation underlying this area was deposited roughly 500 million years ago in a shallow, fluctuating ancient sea. The alternating layers of shale and limestone reflect repeated shifts in sea level—deeper water left muddy shale, while shallower water left carbonate-rich limestone. Centuries later, the Sevier orogeny folded and uplifted these beds, and erosion stripped the surface down to expose different rock layers across the landscape.
• Stalled Collapse: Horse Lake’s basin likely formed through the same karst dissolution and collapse processes that created nearby Peter Sinks. However, while Peter Sinks punched entirely through the limestone to form open drainage conduits, the collapse at Horse Lake stalled when it hit an impermeable layer of shale.
• Holding Water: Because the basin is floored by this tight shale, the lake is entirely dependent on snowfall. The only water loss comes from evaporation and slow lateral seepage where the shale thins or fractures at the margins. There is no vertical drain or open karst throat here—just an ancient, muddy seafloor doing its original job of holding water.
• The Low Point: We did find a small sink at the absolute low point of the basin, though that section is currently isolated by a man-made dam.

• The Logan Canyon road was started in 1862.  By 1869 a toll road ran to Wood Camp, and by 1880s, the road served the Temple Fork Sawmill.  However, a 1892 article in the Logan newspaper noted "The road through Logan Canyon is in a sad condition. In places it is hardly passable. Here and there huge boulders adorn the road, while deep mudholes and dangerous washouts render a ride through the canyon somewhat exasperating . . ."
  
• Subsequent road construction led to two passable routes to Bear Lake. The Meadowville Road left Logan Canyon after 9 miles to follow the Right Fork to Mud Flat and east to Meadowville at the south end of Bear Lake. The Garden City Road left Logan Canyon after 22 miles to follow Beaver Creek and Amazon Hollow, on to Bear Lake Summit and Garden City (Logan Canyon does not continue east toward Garden City, it actually runs north to Franklin Basin in Idaho). 
• Several factors caused the Garden City Road to become the favored route; a dugway was constructed around a challenging section in 1914-1915, travel was hindered by a difficult section on the Meadowville Road above Mud Flat, and local leaders favored the Garden City route because it served the Amazon Mine. 
• The dugway was improved in 1932 and the road was realigned and surfaced between 1935 and 1939 using federal and state money.  Its completion in 1939 marked the first time the road to Garden City could be plowed and kept open year-round, paving the way for winter recreation and the establishment of Beaver Mountain Ski Resort. The old Garden City Road east of Stump Hollow was replaced by a newly constructed US-89 route above Amazon Hollow, although much of that section of the old Garden City Road is still used as a Winter Sports Trail. 

• 14 Hikers, Susan, Dave P., Kathy, Ocean, Lin, Dave W., Jane, Bruce, Sue, Stephanie, Brent L., Teresa, Kamren, Christine, Deb, and Ralph (Leader), and two "amblers", Dave W and Christine.
  
• Drove 28 miles to the Beaver Junction Picnic Area and Winter Trailhead (the amblers drove three miles farther north to hike Sink Hollow)
  
• Started hiking at 8:50 AM, lunch from 11:45 AM to 12:15 PM, returned to trailhead at 2:20 PM
• Mostly sunny, breezy, and beautifully cool for late June
• Hiked about 8 miles with 1800 feet of elevation gain (the amblers walked 2.3 miles with 300 feet of elevation)
  

Thanks to Ralph for the narrative, photos and GPS data, and Jane, Dave P, Christine and Susan for photos..