Mount Si is one of best and most popular hikes near Seattle. The mountain, originally referred to by Native Americans as 'Kelbts,' borrows its current name from a mid-1800s farmer, Josiah 'Uncle Si' Merrit. Due to the close proximity to the city, the trail is often busy with hikers, climbers, and miscellaneous adventurers. Incredibly, this trail sees approximately 80,000-100,000 users per year.
The trailhead's elevation sits at approximately 700 feet, and from here you zigzag through a tall Douglas fir forest with sunlight filtering through the limbs on the well-maintained trail. Don't let the quality of trail fool you, though; it gains over 900 feet of elevation in the first mile. This is a great test for those starting out on Mount Si!
After approximately 2 miles there is a short reprieve at Snag Flats, which is a brief, flat section of trail with a boardwalk and signage that describes the history of the mountain, the trail, and the surrounding area. Be sure to rest your legs here if you need to, as the trail is relentless from here.
Continue about 1,800 feet up the trail from Snag Flats to Haystack Basin, and by now you have reached an elevation of 3,900 feet. This is the end of the trail for most hikers, and it offers outstanding views of the Upper Snoqualmie Valley, the Puget Sound Basin, and the Olympics. There are plenty of areas to rest and eat the lunch you've packed with you, and you'll get great views of the 4,167-foot summit known as The Haystack that hovers about 300 feet above you.
Most will view the summit and return to the trailhead. For the adventurous few who wish to continue to the summit, use caution. Falls on the Class III scramble to the summit are often exposed and can result in serious injury or death. The rock here has been climbed often enough that most of the loose rock has been dismantled.
The there-and-back trip to Haystack Basin on the Mount Si Trail is 8 miles (8.5 for those who summit the Haystack), and it takes about 4.5 to 6.5 hours on average.