One of the things you may have been noticing in the images for Thirty Days is how during the month everything has changed. At the start of November there were still leaves on the trees as well as on the ground and now 21 days into the month of November there is a look of winter more so than fall.
On my way home today, I headed towards Sloans Lake which is located on the western side of Denver. From here you can see part of downtown, however with the sun behind the cloud cover it was not an interesting photograph. As I walked around the lake, I noticed a few people jogging and took advantage of this with a barren tree for the image on Day 21.