The most commonly misspelled peak in Oregon and one of a handful of alpine rock routes, this is a fairly easy day climb. It may look quite challenging from the start, but the technical climbing is just one pitch of easy 5th class rock at the top. Duct taping your boot tops is recommended for the scree descent. An apres climb swim in Diamond Lake is recommended.

Known as “the Lightning Rod of the Cascades”, the striking summit of Mt. Thielsen is the 7th highest peak in Oregon. The peak was named for a pioneer road builder, Hans Thielsen. It is similar in age and structure to Three Fingered Jack and Mt Washington, where glaciation and other types of erosion have left a relatively solid exposed plug of basaltic andesite. The plug is excellent rock in contrast to the rest of the mountain, which is generally poor. There is a small remnant glacier on Thielsen, and thus summiting this peak qualifies one for Mazamas membership. 

The first ascent was done in 1883.  

Activity Notes

Despite its intimidating appearance, a climb of Mount Thielsen is a relatively straightforward undertaking. The West Ridge is an exhilarating route with a short 5th class pitch (5.1) at the top to make things interesting…. not quite technical but with enough exposure to get the adrenaline pumping. There is a small remnant glacier on Thielsen (Lathrop Glacier), and thus summiting this peak qualifies successful climbers for Mazamas membership.


A five-hour drive from Portland to southern Oregon makes this climb tough on a weekend climber.  The Memorial Day 3-Day weekend works out well because of this.  Travel on Saturday, climb Sunday then return on Monday.

Other Information
Driving Distance from Portland 250 miles
Driving Time from Portland 5 hours
General Route Info summitpost mountain forecast
Expected Duration Car to car in one day
Relevant Books Oregon High by Jeff Thomas
Relevant Maps USGS 7 minute series, Mt. Thielsen and Diamond Lake Google map
Useful Links