Narrowleaved evergreens (juniper fall into this category) can maintain foliage for two years or more. Eventually the innermost, oldest foliage drops off.  There are also many scale insects that affect conifers (all these Junipers are actually conifer shrubs).  The area in your photos looks well watered (it looks lush) so I don't imagine drought is an issue in these microclimates.  Could it be?  I don't have a direct answer to your question based on your overview but I would suggest you look closer (micro level) and determine if there is an insect pest.  If not, we can rule that out and go to abiotic factors like weather (sun exposure, drought...)  Also, look at the Aspens.  Are there any indicators that a stressor is in the area?  Obviously you are interested so I think a little further investigating will help you in your botanical exploration.  Check CSU Extension Fact Sheets for research based info on these issues.  Sincerely, Dan