Park at the Marple Mountain Sno Park overflow area which is on the south side of SR83. Plenty of parking room in the non-snow months.
Follow FR8312 to the summit which is about 4 mi one way. Easy hike up an old logging road. The summit is a site of an old firetower but is now used as a USGS Mt St Helens monitoring site. Enough room at the summit for an EFHW. Good vistas of Mt Adams but St Helens is obscured by the forrested summit.
Directions: From Cougar, WA drive east on Lewis River Road, which turns into Forest Road 90. Continue on Forest Road 90 until the intersection with Forest Road 83. Turn left on Forest Road 83 and continue approximately 6 miles to the Marble Mountain Sno-Park. During the winter and early spring Forest Road 83 is gated at the Sno-Park. Note that this area can be crowded in the winter months.
See: http://www.fs.usda.gov/recarea/giffordpinchot/recarea/?recid=64876 for more information.
