Hello there and thank you for using Ask Extension. 

Your photos are quite helpful.  Based upon you photos, the tree is not suffering from a lack of water. If it was, the tips of the needles would be brown, especially the needles at the top of the tree and at the ends of branches.

The tree looks very healthy except for a few areas.  When did you first notice this problem?  Is it getting worse?  Does your irrigation system spray on the needles of the tree? Any digging or trenching in the area that could have affected the roots of the tree?

It could be a needle cast, but that is pretty rare on the plains of Colorado.  Here is some information on the needle cast, Dothistroma sp.  There are other needle casts that affect ponderosa pines also. 

 https://extension.umn.edu/plant-diseases/dothistroma-needle-blight

To obtain a more accurate diagnosis, you would need to bring in a sample into our extension office.  There would be a $7 charge. You would need to bring in a branch that is affected with the possible fungus.  It would be good for us to see a branch with healthy and unhealthy needles.   Here is the contact information.  https://arapahoe.extension.colostate.edu/county-directory-2/

Here is another resource for you to look at. 

 https://extension.colostate.edu/docs/misc/NeedleCasts.pdf

It's a pretty technical document, but it is specific to Colorado.  The narrative on pages 99 and 102 may be quite helpful. According to the document, this disease is rarely fatal, especially if you take good care of you tree, which it appears that you do.   (No need to read the narratives on Brown Felt Blight or Juniper Tip Blights. Those are different diseases.)  

If it's not a needle cast, it could be natural dying of the older needles on the tree.  On Ponderosa pines needles only live 3 to 4 years.  

If you have any further questions, let me know.