I suppose my experience in forestry is why I was forwarded your question about conifers on 9 acres near Soldiers Summit. From Utah Division of Forestry, Fire & State Lands Forest Health 2003 report, Mixed conifer forests occur at elevations from about 8,000 to 10,000 feet. Douglas-fir, white fir, and lodgepole pine are the main tree species in this type. Spruce, subalpine fir, and ponderosa pine may also be a component of mixed conifer forests. Species diversity in this habitat type contributes to wildlife habitat diversity.
Bark Beetle Impacts
In a healthy forest, endemic levels of insects and diseases serve to remove weakened and stressed trees, thus thinning the forest and reducing competition for light, water, and nutrients. Overly dense forests composed primarily of larger diameter mature trees are less vigorous. Such sites are preferred by many species of bark beetles, which contributes to outbreaks. Large-scale insect outbreaks often result in an accumulation of down woody debris,which can increase fire intensity.
Before spraying, it is of utmost importance to have proper diagnosis of tree health. We have been in a drought for 7-8 years in the last 10 years, so browning of needles does not necessarily mean there is a pest issue. Granted due to drought stress, trees do become more susceptible to secondary health issues like beetle infestation or plant diseases. Here are a couple links to Utah Division of Forestry, Fire & State Lands information on bark beetles in Utah.
Ips Bark Beetle
Mountain Pine Beetle
There are recommendations on the fact sheet, again only after a proper diagnosis from a forester or arborist to confirm.