Route 4 stays in northeast Colorado
The plotted Eastern Plains route begins in Boulder, heads to Jackson Lake State Park, crosses Pawnee National Grassland and finishes at Madison-Macdonald Observatory in Fort Collins.
That is intentionally a compact northeast Colorado trip. It does not keep driving hundreds of miles south simply because those destinations happen to share a plains region.
The southeast is still worth its own trip
John Martin Reservoir, Kim and Comanche National Grassland remain in this regional guide because southeastern Colorado can offer enormous horizons and very dark country.
They are not Route 4 stops. Treat them as the backbone of a separate southeast-plains trip if that is the part of Colorado you actually want to explore.
The horizon gets bigger as the map gets emptier
The mountains give Colorado drama. The plains give it scale. With very little terrain blocking the view, a meteor can run a long way across the sky and the Milky Way can arc from one side of the landscape to the other.
If you want a huge sky more than a dramatic foreground, this is the branch to remember.
The local hub changes depending on which plains you choose
Boulder is the Route 4 handoff. Fort Morgan and the I-76 corridor are useful for the northeast. Pueblo becomes the better launch for a completely separate southeast run, with Lamar and La Junta taking over once you are deep into the plains.
There is no reason to combine those two road trips just to make one long line on a statewide map.
Bring what you need
Services thin quickly away from the Front Range and major corridors. Carry water, keep enough fuel in reserve, download maps and know exactly where you are allowed to park or camp.
An empty roadside is not automatically public land or a legal observing site. Out here, self-reliance is part of the observing equipment.