The view of Mt. St. Helens and Mt. Adams beyond from the summit of Goat Mountain, Feb. 2005.
The peak rises steeply on all sides with areas of challenging basalt cliffs on the south, east and north faces. There is a pretty good, brushed-out trail to the summit with just a few logs to scramble over. It is never more than a low class two route and mostly just a steep class one hike. This is a user-maintained bootpath route with a few flags along the way to help you stay on track. Still, it's a pretty good workout rising 1,600 vertical feet in exactly one mile. The steepest section of the route rises at nearly a 40 degree angle. The last 150 vertical and 2/10 mile to the summit is a ridge walk with great views all around. Besides the great views of Mt. St. Helens, only 5.3 miles to the east, Mt. Rainier, and Mt. Hood, the peak offers unique views of the entire SW Washington area and an excellent perspective on the 1980 blast devastation zone. On a sufficiently clear day even the Olympic mountains are visible to the north.
The mountain is covered almost entirely with a primitive old-growth forest and the only visible evidence of logging seems to be a small section on the lower slopes of the west side. Since the mountain is almost entirely within the Mt. St. Helens National Volcanic Monument, it's likely that it will remain in its pristine condition. (The monument boundary is the dot and dash line on the west base of the mountain which is also the approximate edge of the old growth forest. See map and signature pic for photo showing the stark contrast between old growth and second growth.)
From I-5, either direction, take exit 21 in Woodland and head east on State Route 503 toward Cougar. Less than a mile west of the town of Cougar, turn left (north) on Forest Road 81 marked "Merrill Lake". Follow the two lane paved road #81 for 8 1/2 miles to the junction with road # 8117 and take the left fork. Follow this (unmarked) gravel road for 3.1 miles and take a right at the junction (also unmarked). Another 1.7 miles brings you to another (again, unmarked) junction where you turn right again. Park at the saddle in another 4/10 mile. Take the trail up the hill to the east. (Note: The gravel roads are narrow, have abundent world-class potholes in places but also have sufficient turnouts. When not covered in snow and ice this should be navigable by most "normal" vehicles.) .
Note: 120 yards up the hill you will encounter a wide, maintained trail. Turn left and follow this for 35 yards and then turn sharply right on the user trail.
The "maintained trail" aka "Fossil Trail" continues north along the west base of the mountain and starts at the horse camp just east of the junction with 81 and 8117 and would be an excellent early season access route to the peak. The trail is well graded and for the most part passes through ancient old growth forest. However, it would add about 1,300 vertical feet and about 4 miles RT to the climb.
Currently, no parking passes or permits are required at the principle embarkation point or along the road leading to the peak.
When To Climb
Any time of the year but snow will usually limit access and make part of the trip a forest road hike of possibly several miles. As of Oct 1, 2017, the road is snow free and open all the way to the base of the peak though there are a couple of deep ruts that must be navigated with care. If your vehicle is low clearance, you may have to walk an extra half mile or so.
Good camping areas abound at Merrill Lake and many other spots in the area.
Here is the link to the snotel site at Sheep Canyon, just 3 miles NE of Goat Mt. which should approximate mid-mountain conditions: Sheep Canyon
Also, here's another snotel site that should be consistent with trailhead conditions and is located just 7 miles east on the south side of Mt. St. Helens.