Canyon CreekThe most popular hike is probably Canyon Creek. The trailhead is at the end of Canyon Creek Road. From the Bay Area, take highway 5 north to Redding, then highway 299 west for about one hour, 12 km west of Weaverville (or take highway 101 to Eureka and go east on 299 for about 1.5 hours). When you reach Junction City, turn north (right if you are coming from Weaverville) onto Canyon Creek Rd (in 2011 there was a cafe at the corner) and continue for about 30 minutes on the narrow winding road. The elevation is very low: 900 meters.
The trail to the Canyon Creek Lakes (end of the trail) is about 12 kms. I found wildly exaggerated distances on the Web for this region.
Mt ThompsonIf you want to climb Thompson Peak (the highest mountain in the Trinity Alps (alas a mere 2741m) , continue about 8kms cross-country. Thompson Peak is the second prominent mountain on your left (the first one is Wedding Cake). When you reach the last lake, it is not trivial to cross the creek that comes out of the lake. The current is strong so don't try to wade it. Look about 100 meters downstream and you should see a natural "bridge" that crosses the lake downstream. This is mostly boulder and log hopping but it probably saves you from getting wet. Once on the other side, hike up above the boulders that constitute an obvious obstacle for coasting the lake. Most people then descend to the inlet of the lake and hike up the canyon but i think it is more efficient if you stay at the same elevation and continue straight north (basically parallel to the creek but about 200 meters to its right and 200 meters above it). You will come to a roaring tributary that makes an intimiditating waterfall but i found a place where it narrows enough that you can jump it easily. On the other side there are even more intimidating ledges but it is not difficult to climb them, coasting the canyon from higher up. You should end up into the canyon but having saved quite a bit of effort. Higher up the canyon opens into a swampy meadow. Wedding Cake and Thompson are now clearly visible. There is usually snow here even in the summer. I take to the right and climb the prominent cliff that takes me straight up to the plateau under Thompson. From this point the slope is reasonable even with snow up to the crest between Wedding Cake and Thompson. When you reach the crest, turn right and coast the crest to the left (north side) but stay near the crest. When you get to the summit block, there are two relatively easy ways to climb it. There are several USGS markers on the very summit.
Mt EddyIt is not technically part of the Trinity Alps, but while you are there you might as well climb the highest mountain west of highway 5. Mt Eddy (2751 m) can be reached from this trailhead: Take exit 751 of hwy 5 toward Edgewood/Gazelle, turn left onto Edgewood Rd, turn right onto Stewart Springs Rd. Take the first major right turn to stay on Stewart Springs Rd (otherwise you end up to the gate of a tourist resort). This is forest route 17 (several signs). Continue for about 10 kms. The trailhead can be a bit confusing because (in 2011) the sign is barely readable. There is a fire road to the left of the trailhead. The trailhead is not very visible but it is a mere trail, so if you get to a fire road look 10 meters to its right. The hike is 16 kms roundtrip (3 hours up, 2 hours down). It falls under the Mount Shasta Ranger District.
Pacific Crest TrailA recommended route begins at the Scott Mountain Campground just off Highway 3 at Scott Mountain Summit. The trail-end is at Carter Meadows Summit on Forest Highway 93.