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16 miles

Elevation Gain

4500 ft

Route Type



Added by Gabe O'Leary

This impressive looking summit stands out to all hikers in the area. It has the best view within a day's hike of Snoqualmie Pass

The West Ridge of Thomson is rated 5.6 and is 4-5 pitches depending on how you break it up. The East Ridge is some spicy 4th class and although people do scramble it, it is recommend to use a rope on the descent.

The Approach

Starting at the PCT trail-head you have two options.  You can take the PCT the whole way which is a bit longer and wastes a bit of elevation or you can take the Old Commonwealth Basin Trail shortcut.  To take the shortcut, start out on the PCT and make your first left turn.  Follow this trail until it crosses a creek on a log bridge.  Then turn right and continue until you get to another creek.  This creek has no bridge but there are sometimes logs you can use to cross.  From there follow the trail until it joins another trail at which point you should take a right and then after a short while take a left and you are back on the PCT having saved yourself some time and distance (assuming you didn't get lost).

Once on the PCT follow it for quite a few miles, you will take many switchbacks and eventually cross the Kendall Katwalk, a popular destination for day hikers.  Continue past the Katwalk until you reach Ridge Lake.  If it's late in the season this is the last place you will be able to fill up on water (earlier in the season there is running water in the basin below Thomson).  From Ridge Lake continue for 1/2 a mile until you see a steep and rocky climbers trail on the left side of the PCT.  This leads to Bumblebee pass where you begin your descent in to bumble bee basin below Mount Thomson.

West Ridge

From the basin head up and to the left to the lowest notch west of Thomson's west ridge.  From here it is 4th class scrambling around a series of Gendarmes to reach a notch at the base of the climb where you will rack up. The first pitch has one "5.6" move off the ground that I found to be pretty easy.  The rest of the pitch is low 5th and brings you to a tree belay.  There are several options for the 2nd pitch but be mindful of rope drag and make sure to extend your pieces. You can finish the 2nd pitch at ledge system and use cracks or boulders to build your anchor.  The 3rd pitch is low 5th and 3rd class scrambling along a large slab which will take you to some more trees which provide a good anchor.  The 4th pitch can be climbed as 1 or 2 if you don't like the rope drag.  It is mostly low 5th with an interesting layback move midway up.  At the top of this vertical section you can coil the rope for the scramble to the false summit and beyond to the true summit.  From the false summit the last bit to the true summit looks intimidating but if you skirt around to the left side of the ridge it is 4th/5.0 to the summit.  Most do not use a rope for this section.


To descend walk off the east end of the summit until you see some trees and a rap anchor.  Make sure to check the anchor and replace the tat or rap rings if needed.  2 raps are recommended to get down the east ridge.  It looks like manageable down climbing from above but is considerably harrier than it appears.  At the bast of the second rap walk left until you see a trail down through some trees.  There is a 3rd rap anchor here but it is not really needed as it's just 3rd class down climbing from here. From here the trail goes in and our of choss and takes you around to a notch in the ridge.  The rock is unpleasantly lose here so take care not to knock rocks down or your party members or others. From the notch descend into the basin and retrace you route back up to bumblebee pass and along the PCT back to the car.

Bivy Options

  • Along the PCT between Kendall Katwalk and Ridge lake there are many tent sites. 
  • For more seclusion you can bivy in Bumblebee basin with great views of Thomson, Huckleberry, Chikamin, Lemah and others.  There is running water here though most of the summer.
  • For the ULTIMATE bivy, bring your gear all the way to the summit and sleep on top! We were more than comfortable with 2 up there, you could probably manage with 3 no problem.


If you find yourself with some extra time and energy after Thomson you can continue up the PCT to tag on the summit of Alaska Mountain.  Follow the PCT all the way to it's East Ridge and try to stay on the ridge crest on some superb rock.  The Ridge takes you all the way to the summit.  You can retrace your steps or cut due south to return the PCT from here.

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