Complex sentence: When a couple hundred miners who had come for the Clearwater Gold Rush of 1861, heard of a huge bonanza there many of the miners walked from Pierce, Idaho to Florence in the dead of winter.
Split into simpler sentences: When a couple hundred miners who had come for the gold rush, in clearwater gold rush of 1861, heard of a huge bonanza. Many of the miners walked the from Pierce, Idaho to Florance in the dead of winter.