The two perennial water sources are Kangaroo Springs along the PCT and Lonesome Lake. Make sure to stock up. The trail also has significant southern exposure without minimal coverage. Plan accordingly for water and the elements.
The Red Buttes Boundary Trail connects the PCT: Seiad Valley to Highway 5 (near Ashland, OR)
to the northern Greyback Ranges. It is part of the Red Buttes Wilderness, which is named for the higher iron/magnesium content in the serpentine and peridotite formations prevalent in the area. Along the trail you'll have views ranging southeast to southwest, covering Mt. Shasta and the Marble Mountains and west to parts of the coastal range.
From Kangaroo Springs, you'll follow the PCT up a small series of switchbacks out of the basin. Just under 1 mile from Kangaroo Springs, the PCT will take a 270-degree turn left and the boundary trail will continue forward. At the time of this writing, the signpost was present, but no longer standing.
Straight ahead will be the boundary trail along the southern edge of the ridgeline for the most part. For the next 2.5-3 miles, you'll hike beneath views of Desolation Peak and Rattlesnake Mountain. From here, you'll descend through a series of short switchbacks, working around a southern formation and back onto the ridgeline headed west-northwest.
At about 3.5 miles, you'll crest a saddle where you have beautiful views both north and south. On a clear day, you'll be able to see Mt. McLoughlin, Mt. Shasta, and down into the Trinity Alps and Marble Mountains. There is a rock pinnacle here that is great for panoramic photographs.
Continuing on, you'll eventually travel around the southern edge of Goff Butte before intersecting with the Fort Goff Trail. At this point, you'll be about 6.5 miles along the Boundary Trail and 7.5 miles from Kangaroo Springs. At the intersection here, you'll be able to hear and see the creek coming off Lonesome Lake, and either this or a short 0.25-mile hike to Lonesome will net you a reliable water source.