About 500 million years ago, Vermont was part of Laurentia and located in the tropics. The central and southern Green Mountain range include the oldest rocks in Vermont, formed about one billion years ago during the first mountain building period (or orogeny). Subsequently, about years ago, the second mountain building period created Green Mountain peaks that were tall, three to four times their current height and comparable to the Himalayas. The geological pressures that created those peaks remain evident as the Champlain Thrust, running north–south to the west of the mountains (now the eastern shore of Lake Champlain). It is an example of geological fault thrusting where bedrock is pushed over the newer rock formation.