Steve's Coast Starlight
I consider the Starlight one of the most scenic train rides in the world. Althought the north and southbound trains travel the same route, it is different in each direction--due to time of day, direction of travel, and other factors. On my Web site, I have (more or less) described the route from north to south, but eventually I want to do a northbound version, as it is different. My comments are based on traveling during the summer months and with the possibility of the trains' lateness--the Starlight does have a reputation for lateness. This is not to disparage the train for that but to use the lateness to advantage.
Southbound (leaving Seattle at 10am), you will be able to see more of the green, Western Washington valleys and Mount Rainier (on clear days--to the left); the ride along the Puget Sound (south of Tacoma--to the right) is my favorite part of the route between Seattle and Portland. Northbound, the train is supposed to arrive Seattle at 8:30pm--still plenty of light during the summer--but the train can be one or more hours late, making much of the journey between Portland and Seattle during darkness.
Southbound continuing: it is still daylight through the Willamette Valley and through the Oregon Cascades (even if the train is up to and hour or so late), but it is dark by the time the train gets to Klamath Falls. It is dark until about Roseville (northeast of Sacramento and where the Starlight route meets with the Zephyr/Overland route). It should remain light until at least Santa Barbara (even if the train is a couple of hours late); the ride along the Pacific Ocean at sunset should be stunning--to say the least. Northbound, you'll have daylight until at least Salinas (if the train is up to a couple of hours late). Daylight should be appearing again north of Redding (perhaps including Redding) and the train's crossing of the Redding Trestle and the snaking through the Sacramento River Canyon to Dunsmuir. The sun will probably be quite up by the time the train leaves Dunsmuir. The train snakes around and climbs along the flanks of Mount Shasta--and it is spectacular watching the sun com up and shower its (changing) light on the mountain--and as the train goes around, gets closer, goes farther away, the mountain takes on different shapes and shades of light, etc. Grass Lake (elevation 5,063 ft.) is the highest point on the route of the Coast Starlight. It will be daylight and scenic past Klamath Falls, descending the Cascades, and onto Portland (at least--usually).
Southbound--even during the darkness, you can sometimes follow the train's path by using the locomotive's headlight and the train's lights. The full moon will sometimes illuminate Mount Shasta.
This is all based on summer daylight averages; winter hours will have its own problems. Southbound, you should be on the right side (left side going north) of the train if you want to look at the water (Puget Sound, Columbia River, San Francisco Bay, Pacific Ocean), the left side (right side northbound) if you want to see the Cascade Mountains. Of course, there are usually nice things to see on both sides of the train, sometimes at the same time.
