Defoliated Lilac

Your lilac certainly doesn’t look happy. While it’s normal for them to lose their leaves for the winter, the remaining leaves on your plant look a bit wilted. And then there are all the bare branches. Too much water can cause wilting, as the roots drown. Roots need as much air as they do water. Lilacs only need about an inch of water per week.
Another possibility is unintended side effects from broad-leafed weed killers. Lilacs are broad-leafed plants, and the weed killer used on a lawn doesn’t distinguish between lilacs and dandelions. Have you applied any turf weed killers near your lilac?
We suggest you prune out the dead stems at ground level. Then, in early spring, feed your lilac at about half strength with a high nitrogen fertilizer (fish emulsion is great). Most Colorado soils have plenty of potassium and phosphorus. Add a couple of inches of mulch around the base of the shrub, leaving a gap near the “trunk” so the stems don’t rot. We hope that helps!