Lodgepole Pine and Engelmann Spruce
Normally, these two species of soft woods are mixed together in milling processes as they are grown together in the same timber stands. They are both light colored woods with knots of various sizes. Only the trained eye could pick out one species from another in a log wall.
The spruce is a little softer wood and thus has a slightly higher R factor due to its porous nature. These two species grow over a wide range throughout the Western United States and Canada.
If you like lighter colored log walls for a bright appearance, then these species would be the ones to choose. Due to the soft nature of the wood, they work well for nailing, spiking and attaching other fasteners to the walls and beams during construction.
These also mill very well with a nice smooth surface being the final result. The smooth milling is also obtained from the use of dry stock for the log material and the use of Tungsten Carbide cutter heads during the milling.