The Sierra Nevada Mountain Range: Brief History of the Sierra Nevada's

(source: http://upload.wikimedia.org/wikipedia/commons/2/23/Chinese_railroad_workers_sierra_nevada.jpg)

Seeing how this ecosystem is a mountain range, there is not a lot that humans can do to destroy it. The granite that these mountains were mainly formed from is an incredibly strong rock, that does not erode very easily. The early Native American and Spanish explorers of California had almost no impact on the ecosystem. These people lived off the land and had hunter and gatherer preferences or very small settlements that did not take away from the mountains.

The first notable non-natural degradation of the land came from the Gold Rush that began in 1848. This Gold Rush caused people to begin dredging rivers and streams from the snow melt, blasting and digging out mines, and removing trees to make way for roads and settlements in the mountains. Historically, the gold rush was the catalyst for most of the damage that has occurred to this vast ecosystem across its lifetime, however the damage left was not very prominent across the range as a whole. This was due to the facts that with the mines and hunt for gold, a need for railroads and streets came into being. Roads were formed to connect mining towns to their mines and prospect sites, while railroads were used to connect these Northern settlements with the major cities like Sacramento and San Francisco. The building of these means of transportation involved the removal of trees, boring of tunnels, and carving and construction of flat land across the mountainsides. These railroad lines still exist today, albeit they have probably been restored and more modernized. Mining roads have also no doubt been paved over and put to a more modern use, for it was this California Gold Rush that truly brought larger amounts of settlers into these mountains.

Despite all this work however, historically speaking the human impact in this ecosystems has been quite low. Many of the special areas in this ecosystem were protected before major damage could befall them, and a large amount of the ecosystem is also protected under the Wilderness Act. Outside of the roads, ski resort cities, Gold Rush damage, and stream reinforcement efforts, this is an ecosystem that has been largely undisturbed by humans. because of this, I would have to say that historically the environmental impact has been good.