It was the obstacle that the California-bound pioneers feared the most: crossing the formidable Sierra Nevada. Stretching from just below Lassen Peak in the north to Tehachapi Pass in the south, the Sierra is a single mountain range about 400 miles long, varying in width from 40 to 80 miles. Except for the angle of the state of Nevada which cuts through Lake Tahoe, all of it lies entirely in California. Following a series of geologic upheavals over a 100-million year period, the Sierra as we know it today began forming about 10 million years ago, when a block of crust between the Coast Range and the Great Basin started to uplift and tilt to the west. Eroded over many millennia into a range of rolling low mountains, rivers began cutting deep canyons; two million years ago during the ice ages, glaciers carved out the characteristic U-shaped canyons found throughout the range. Dotted with scores of small lakes and filled with acres of pine, redwood and conifer, most of the area is protected from logging and grazing by the United States government. Ranging from 5,000 to over 14,000 feet, the Sierra is a barrier to the winds and storms that blow from the Pacific Ocean, casting a “rain shadow” which is largely responsible for neighboring Nevada being the driest state in the Union. Uplift of the Sierra Nevada continues today.