My field season is over now, but I could tell it was time to go. We tell the time by reading our organisms and need no calendar.

In the high Rockies, the meadows have begun to die back – late season aspen sunflower (Helianthella quinquinervis) and silver lupine (Lupinus argenteus) blooms struggle along, but all else is turning a dusty shade of green-yellow.

Only at very high elevations is summer continuing. Here at 13,600′ elevation, an old man of the mountain (Hymenoxys grandiflora) is blooming, but colder and shorter days will soon put an end to this display.

Lower down, wild strawberry (Fragaria virginiana) has long discarded its flowers, and has seen many of its fruits eaten and seeds dispersed by its many consumers.

The autumn fungi have emerged after a period of heavy rains. Here a fly agaric mushroom (Amanita muscaria) displays an immature fruiting body.

And, a sure sign of fall, the marmots (Marmota flaviventris) have grown to an enormous size, putting on fat in preparation for the winter to come. Pictured here is the family that lived next to my cabin – Dandelion (who looks like he ate a watermelon), Stitches, and Question Mark, all tagged for long-term research by UCLA biologists.

Year-to-year, the relative timing of these signs of autumn shift, and sometimes are delayed or advanced compared to a standard solar calendar. Many of these phenological shifts and potential mismatches may be linked to ongoing climate change (Inouye 2008) and are actively being investigated by many researchers.

But for me, it’s enough to mark the passage of the seasons roughly by these living cues, and to make the transition from days on the mountain to days in the office, analyzing a summer’s worth of hard-earned data.