September 18, 2025
Color Change: 65% (High)
Leaf Drop: Low
The fall colors are arriving in Spearfish Canyon. Autumn foliage is currently at 65% of its peak, or fullest color saturation.
The tree-lined road at the entrance to Spearfish Canyon is bursting with golden ash, box elder, and birch. We continue to see some lighter greens until Bridal Veil Falls. Look west of the Falls where you’ll see yellow birch and hophornbeam amongst the volcanic rock. The red sumac northeast of Botany Bay is reaching 80% of peak. Foliage is also reaching peak colors around Kissing Rocks.
The countdown is on until the first day of fall on Monday, September 22, 2025. Fellow leaf watchers, prepare to enter the “photoperiod.” The photoperiod is especially important to the leaves’ color change. Photo means light. So, we are talking about the periods of light (or day length) as we transition into the fall season.
First, daylight is gradually becoming shorter as we enter fall. This tells the leaves to slow down in making chlorophyll. Chlorophyll gives the leaves their green hue. As chlorophyll production decreases in the fall, the leaves slowly reveal their true colors, the brilliant golden hues we see in the deciduous trees in Spearfish Canyon.
In my next report, I’ll tell you the second most important factor that influences when the leaves reach their “peak” or most vibrant colors. Stay tuned!
