The last frost date in Colorado varies significantly by location due to elevation and climate differences. Here are some average last frost date ranges for selected locations in Colorado:

• Most locations around Denver, Aurora, Boulder, Fort Collins, and Greeley typically experience their last frost between May 11 and May 20.
• Some areas like Castle Rock and Durango have a later average last frost date, around May 21 to May 31.
• High elevation or mountainous areas such as Black Forest may see their last frost occur as late as June 1 to June 10.
• Other western Colorado towns such as Grand Junction and Clifton tend to have earlier last frost dates, around April 21 to April 30.
• In Colorado Springs, the last frost is generally around May 11 to May 20.
• Specific extreme cases show the last frost in places like Aspen or Crested Butte happening as late as mid-June or even July in rare years, but the average falls in May or early June.

So, the last frost across Colorado generally ranges from late April in lower elevations to early or mid-June in higher elevation areas, with the most common average last frost dates for many populated areas falling in mid-May.