The conifers on the south side of the Rio de Los Pinos between Big Horn and Toltec are mostly Douglas Firs (which, incidentally, are not a true Fir tree). They have been infested with the Pine Bark beetle for years. They aren't as evident now because a lot of the snags have actually fallen down. Aspen are colonizing some of those areas where the forest canopy has opened up (aspen need a lot of sunlight).
On the north side of the Rio de Los Pinos (the side where the railroad is), the slopes face south and are drier, especially east of Toltec to around MP303. That is the preferred domain of the Ponderosa pine. In most of that particular area, the Ponderosas are actually better spaced and are not overcrowded. As a result, they have not been badly affected by beetle infestations. Starting a ways east of Toltec and working west, the altitude is high enough that white fir and aspen tend to dominate until one gets near Osier, where one starts into the spruce/subalpine fir life zone (a regional variant of Subalpine Fir, the Corkbark Fir, is found only in the southern Rockies, and is very common in the spruce/fir zone on Cumbres). Quaking aspen ("quakies" to Rocky Mountain region natives) range extends from the mid and upper elevations of the Ponderosa forests up through the mid-elevations of the spruce/fir forests.
One of the really cool things about riding the Cumbres & Toltec for its whole length from Antonito west is that one begins in the sagebrush steppe of the San Luis Valley (by the way, Antonito is actually slightly higher in elevation than Chama--but doesn't appear like it from a vegetation standpoint because it sits in rain shadow of the Eastern San Juan mountains), up through the Piñon/Juniper woodlands, Ponderosa forests, Aspen/White Fir forests, spruce/subalpine fir/aspen forests, along with the fire-bred open meadows ("parks" in Western nomenclature) to Cumbres; thence westward and downward, through the same life-zones to Chama, but on the wetter western slope of the Eastern San Juans (though the entire railroad is east of the Continental Divide--Cumbres Pass is NOT on the Continental Divide, not withstanding that the Continental Divide Trail is on the pass). Large groves of Gambel Oak (known in the region simply as "oakbrush") grow on the wetter western side of Cumbres Pass as one exits the Narrows and approaches Chama, compared with similar elevation areas near Antonito's drier eastern side that is dominated by sagebrush.
Just as a ride on the C&TS is a fascinating study of geology, it is equally fascinating as a study of mountain forest ecology. And, unlike roaring through the countryside at highway speed in an automobile, the leisurely pace of the train allows one to actually see the myriad of plants that make up a very complex forest ecosystem.
