Tuesday, September 11, 2007
Pilchuck Mt. offers scenic hiking near Seattle
Flat-Topped Mt.Baker, in the Cascade chain, lies north of Pilchuck
3nd Son finds Pilchuck moderately better than the 120 degrees sands of IRAQ
Fourth Son Steve hikes Pilchuck regularly
Parallel Fractures orient east to west
Pilchuck Mountain: a granite uplift surrounded by extrusives
Hiking on the closest mountain to the Seattle area may be accessed by taking hiway 2 off Interstate 5- I5- near the town of Marysville, WA. This junctions hiway 9 and 92 to Granite Falls near the village of Verlot (where a hiking permit must be bought from the US Forest Service). Pilchuck is south of the South Fork of the Stillaguamish River, and may be accessed via a gravel road, east of Verlot- which was an old ski lift road. This gravel road becomes paved in its upper section, and it ends at the hiking trail. A hike of 3 miles is necessary to find the ski area remains and the tree line at about the 4400 feet elevation. The trail starts at the 3250 foot level.
The whole area exhibits granite-like rocks, and is anomalous in this area of the Cascades extrusives (volcanoes- either dormant or active). The rocks are not only light in color (see the above photos), but are intrusives- as compared to extrusives to the east and metamorphic outliers to the west. The nearby town of Burlington has a metamorphic hill in an otherwise swampy terrain, which is a result of movement of the San De Fuca plate jamming into the continent (creating the ongoing Darrington faulting on the north fork of the Stillaguamish River.).
Even though the Darrington fault is some 15 miles north of Pilchuck, a common stress feature is exhibited in the granite- there are E-W fractures, similar to the orientation of the large fault. This indicates that the stress which created both features is spread over a wide area. One would expect to find N-S faulting (and indeed the Darrington fault does turn south near the town- renamed due to several faults junctioning there), due to the general trend of the Cascades being N-S. Subduction volcanoes orient perpendicularly to the direction of subduction- which is E-W in this case, for the San de Fuca plate. See the photo above which shows the N-S fracturing.