Because you are prohibited from crossing into Canada, this section is a 30 mile out-and-back route. There are no resupply options, but you can leave something at the Harts Pass bear locker for when you return. There are ways to get off this trail but there are no quick bail-out options.
This section has the most high ground, over 6,500 feet of any other section in the state. While it does not have the highest point on the WA PCT, the trail does peak rise above 6,500 ft in five places. And while the average elevation change for this section is low, there are several steep but very short climbs.
The highest point in this section (6,972 ft) is only 2.34 miles north of Harts Pass, after you pass under Slate Peak.
You should not expect mobile phone service on any part of this section, though you may find a lucky spot. There are two towers in Mazama, one just a few feet NW of the Lion's Den, and the other on Flagg Mountain. If driving, you will likely lose service after you pass west of Monument Creek Trailhead on the road to Harts Pass.
The road to Harts Pass is 10 miles from River Bend Campground. It climbs 4,200 ft on a dirt and gravel road with no rail. The upper half of the road is easy. The lower half has boulders and sheer drop-offs (like the 850 ft drop off at Deadhorse Point). Instead of driving it yourself, you might either hitch up, or get a ride From the Lion's Den. The road from Mazama is paved up to the Lost River Bridge.
There is no running water* (caveat below). Trailers are prohibited. Vault toilet. Two bear lockers (near the ranger station which is usually closed). The campground has 5 sites and does not take reservations. It's $10 per night, $15 if you have two vehicles.
The road that heads south goes to Meadows Campground 1 mile away where there is another vault toilet and 14 camp sites, also no reservations. That road continues to the Brown Bear Trailhead, 1.7 miles away.
* Unreliable water near Harts Pass. 0.38 miles northbound from the trailhead there is a trickle stream that crosses the trail here 48.72417, -120.66439. You may be able to collect water there.
If the Slate Peak Road is open, there is an option to start 1.34 miles north of Harts Pass from a small parking lot.
The Harts Pass weather station is 0.5 mile east of the ranger station so you can get very local readings.
There seems to be a lot of ranger patrols in this section, and they will make you carry the free "permit" that you self-issue at the trailhead. I think the main point of this is ensuring you register at the trailhead.
[0 miles] You will want to start with enough water for at least 6 miles.
[5.28 Miles] Be prepared for possible high winds, especially on a northbound approach to the appropriately named Windy Pass. Once over Windy Pass winds should calm.
[5.87 miles] When you are NE of Tamarak Peak the trail will cross a trickle creek here 48.77687, -120.72137 where you should be able to collect water. This is before the 90 degrees turn that begins the switchbacks up the ridge. You will need enough water for at least 6 miles. There is also a nice campsite just upstream from there (see GE).
[6.22 Miles] Tamarack Pass 6,710 ft. (North of Tamarack Peak) is about where you will enter the Pasayten Wilderness which extends to Canada.
[7.41 Miles] At Foggy Pass you will switch over to the west side of the ridge, then back to the east side again at Jim Pass.
[10.1 Miles] After you get over the NE ridge of Jim Peak/Devils Backbone you will want to water-up at Shaw Creek. Check FarOut to be sure the spring 5 miles ahead is flowing.
From Shaw Creek to the base of Holman Peak the forest is denser. You will lose 1000 ft over two miles as you descend to Holman Pass [13.5 miles] , the low point of this section at 5,133 ft. Ironically there is no water here.
[15.7 Miles] There is a campsite on the SW side of Holman Peak with a reliable spring. From there you can traverse (no elevation change) to a lake south of there 0.4 miles away, as a optional side-trip. From here you will want water for at least the 9 miles to Hopkins Lake.
[16.9 Miles] Ironically, Rock Pass is much closer to Holman Peak than Holman Pass and requires a 1,376 ft climb to get from one to the other. Rock Pass is 6,509 ft.
Between Rock Pass and Woody Pass you will lose 890 ft and regain 1,028 ft. over 2.67 miles. After a step traverse of Powder Mountain you will gain 800 ft in 1.1 miles from "Rock Creek" (most likely a dry creek bed) to Woody Pass. This may be the steepest mile in this section. Be sure you stay on the new PCT; About halfway up there is another well-worn trail that goes off to the N/NE. That is the Rock Creek Trail. Some people take the 0.7 mile side trip to Coney Creek in search of water, but I do not recommend it. Ironically, Woody Pass has no trees.
[19.4 Miles] After Woody Pass (6,651 ft) there’s a pleasant 2.5 miles of traverse with minimal elevation change before the short climb toward Devils Stairway.
[22.5 Miles] The second highest point in this section is just before Devils Stairway, 6,760 ft. The lowest switchback of Devils Stairway is pretty sketch, so I am happy to get past it and onto the sharp ridgeline.
[23.8 Miles] 1.4 miles to Hopkins Lake 600 ft below, which is a lovely place to camp and get water. From the ridge north of Hopkins Lake you can almost see the Canadian border.
[24.1 Miles] From Hopkins Pass the last 8 miles to the Canadian border are a steady downhill losing 2,513 ft, which of course need to be regained on the way back. Some people choose to drop their pack at some point along the way knowing they need to back-track. The south side of Hopkins Pass is a good place to do that if you are sure you can cover the out-and-back distance before you need to sleep.