Placer County runs between the Sacramento Valley and the Sierra Nevada mountains, against Sacramento County in the west and 100 miles east to Lake Tahoe. Along the present-day southern border, gold was discovered in 1848 by James Marshall at John Sutter's lumber mill, leading to the California Gold Rush. This relatively narrow county (only 10 to 15 miles across in some spots) has early immigrant trails, wagon roads, railways, and highways all passing through as they head across Donner Summit and across the Sierra Nevadas. Mining, agriculture, transportation, logging, and recreation made Placer County important in the past, and they keep it a thriving place to live now in the 21st century.