The Pumpkin Pie 5k/10k is such a fun race. I've run it every year for the past 5 years.
First off their race Tshirt are AWESOME. Super soft with the cutest designs. This race is super inexpensive compared to a lot of other Thanksgiving themed races. It's held at City park in Denver. It's awesome that you can park at the zoo or the Nature and Science museum. They have a two day packet pickup which is fantastic so you can avoid getting up super early to get your packet on race day . The 5k is one loop of the park and the 10k is two loops. It's a fast and flat course. Afterwards you get the coolest medal and a delicious piece of pumpkin pie with whip cream. If you're looking for a well run organized Thanksgiving themed race this is the one.