This is a late report, but one was observed in the Pueblo Mountain Park (just south of Beaulah) last week on the 4th:
So there are at least TWO along the eastern edge of the mountains right now.
If you live near pondarosa pine forests -- especially with some scrub oak / gambel oak in the understory -- then definitely familiarize yourself with these birds and their vocalizations!
There could very well be more than two lurking in the foothills of the Front Range, Wets and southern Sangres. :-)
Online Grace's Warbler resources:
2. Some basic information:
Good birding,
Paul Hurtado