hiking · hard
Mount Si
- Distance
- 12.90 km
- Elevation
- 1100 m
- Duration
- 5.0 h
- Season
- Mar–Nov
Mia here. Mount Si is the trail every Seattle-area hiker eventually grinds out, and for good reason — it's a steep, sustained climb in a working forest with a payoff view of the Snoqualmie Valley and the Cascades beyond. It's also the trail every Seattle-area hiker complains about, because the parking lot fills before breakfast and the tread takes a beating year-round.
The trail
From the DNR trailhead off Mount Si Road, the path starts gently through second-growth Douglas fir and bigleaf maple, then settles into the kind of relentless switchbacked grade that defines this hike. Across roughly 12.9 km out-and-back with about 1100 m of gain, you climb almost continuously — there are no real flat recovery stretches until you near the top.
Around the halfway mark you'll pass the Snag Flats interpretive area, a small bench of older trees that survived the 1910 burn. Above that the forest gets a little airier and the rockwork in the trail tells you it's seen heavy traffic. The grade eases briefly at the Talus, an open boulder field with the first real view east toward Rattlesnake Ridge, then pushes up to the Haystack basin where most people stop, eat a sandwich, and turn around. The summit proper — the Haystack itself — is a Class 3 scramble that has killed people. Skip it unless you know what you're doing on exposed rock.
Plan on roughly 5 hours car-to-car at a steady pace.
When to go
Mount Si is hikeable most of the year, but the experience changes sharply by season:
- April–June: Trail is in good shape low down, but the upper switchbacks and the Haystack basin can hold snow and ice well into May. Microspikes are not a bad call in shoulder season.
- July–September: Prime conditions and peak crowds. Get to the trailhead by 7 a.m. on weekends or accept the overflow lot and a long roadside walk.
- October–November: Quieter, often wet, leaves get slick on the steeper pitches.
- December–March: Snowline can drop to the trailhead. The grade plus packed snow is a real fall hazard. Traction and poles, not optional.
What to know before you go
- Pass: A Discover Pass is required for the trailhead lot. Day passes are available at the kiosk; bring cash or buy online ahead.
- Parking: The main lot fills early on any decent-weather day. There's an overflow lot down the road, but it adds road walking. Don't park on shoulders posted as no-parking — they tow.
- Water: There are no reliable on-trail water sources you'd want to filter from in the dry months. Carry what you need for a 5-hour climb — most people underpack here.
- Navigation: The main trail is obvious. The hazard is the Haystack: people scramble it in trail runners, get cliffed out, and need rescue. If the rock is wet, don't even consider it.
- Wildlife: Black bears are present but rarely an issue. The bigger nuisance is mice and jays at the lunch spot — don't leave a pack open.
What to bring
Treat this as a real mountain day even though it's an hour from Seattle. The grade chews up shoes and knees, and weather at the top can be 10–15 degrees colder than the trailhead with serious wind.
- Sturdy trail runners or light hikers with grip — the tread is rooty and rocky
- Trekking poles, especially for the descent
- Layers: a wind shell at minimum, plus an insulating layer for the basin
- 2–3 liters of water per person; more in summer
- Real food, not just a bar — this is a 5-hour effort with sustained climbing
- Headlamp if you're starting late in shoulder season
- Traction (microspikes) November through April, sometimes longer
Variations
- Shorter turnaround: Snag Flats makes a reasonable lower goal if conditions are bad above or you're pacing someone new to steep trail — about a third of the climb in.
- Little Si: Across the valley, a shorter, lower-angle hike that's a good rainy-day or recovery-day alternative from the same area.
- Teneriffe add-on: Mount Teneriffe shares a trailhead complex and offers a longer, quieter day with similar gain. Strong hikers occasionally link the two, but it's a long outing and shuttle logistics matter.
- Haystack summit: Adds maybe 30 minutes and a Class 3 scramble. Dry rock, no crowds backed up below you, and a willingness to downclimb what you went up — otherwise leave it.
Common questions
- How hard is Mount Si compared to other Seattle-area hikes?
- It's one of the more demanding day hikes close to the city — about 12.9 km round trip with 1100 m of gain on a near-continuous grade. If you can do Rattlesnake Ledge comfortably, Si is the logical next step up, but expect roughly double the effort.
- Do I need a permit or pass to park at the Mount Si trailhead?
- Yes, the DNR lot requires a Washington Discover Pass. You can buy a day pass at the kiosk or get an annual pass online ahead of time — we'd recommend the latter since the kiosk isn't always reliable.
- What time should I arrive to get parking on a weekend?
- By 7 a.m. on any decent-weather Saturday or Sunday in summer, earlier on holiday weekends. After that you're looking at the overflow lot and added road walking, and shoulder parking gets ticketed and towed.
- Is it safe to scramble the Haystack at the summit?
- Only if you have real Class 3 scrambling experience and the rock is bone dry. People die on it most years after underestimating the exposure — if you're in trail runners and unsure, the basin below is the right turnaround.
- Can I hike Mount Si in winter?
- Yes, but treat it as a winter mountain hike. Snow and ice routinely cover the upper switchbacks from November into April, and the sustained grade plus packed snow makes a slip a real fall hazard — microspikes and poles are the minimum, and consider an ice axe for verglas conditions.
- Are dogs allowed on Mount Si?
- Dogs are allowed on leash. The trail is hard on paws — rooty, rocky, and long — so we'd skip it for dogs that aren't already conditioned to steep all-day efforts, and bring extra water since there's nothing reliable on trail in summer.
- Is Little Si or Mount Si the better choice for a first-time hiker?
- Little Si, without much debate. It's shorter, much less steep, and shares the same general area, which makes it a reasonable intro to PNW hiking. Save Mount Si for after you've done a few hikes in the 600–800 m gain range.
