In May of 1914, Lassen Peak began a seven-year series of eruptions including a humdinger in 1915 when an enormous mushroom cloud reached seven miles in height. Today, the 106,000-acre Lassen Volcanic National Park serves as a compact laboratory of volcanic phenomena and associated thermal features (mud pots, fumaroles, hot springs, sulfurous vents) with Lassen Peak (10,457 feet) near the center of the park's western half. Lassen Peak and its trail up are non-Wilderness, but almost four-fifths of the park has been designated Wilderness, a land of gorgeous lakes teeming with fish, thick forests of pine and fir, many splendid creeks, and a fascinating hodgepodge of extinct and inactive volcanoes. Best of all, this mountainous country remains relatively uncrowded by California standards. At least 779 plant species and numerous animals have been identified here. The eastern border is shared with Caribou Wilderness, and one trail crosses the boundary. About 150 miles of trails snake through this Wilderness. A 17-mile-long section of the Pacific Crest Trail crosses from north to south. Open fires and pets are not permitted on the trails.