While we were in Basalt, we walked along the Basalt history tour and found it very interesting. Why is this not shown as an attraction on Trip-advisor?
Welcome to the forum. It's probably not listed because the business operator, which I think is the Basalt Chamber of Commerce, hasn't listed it. If you enjoyed your experience, you can still do a review of it and indicate that the business is not listed. TripAdvisor will then investigate.
Basalt is a great little town that is often overlooked.
Yes, if you look toward the right of the green bar at the top of the page, you'll see "Write a Review." Click that and you can either go directly to add a listing, or you can click "review a place you've visited." It will search for your place and then ask you to "tell us more about it" and they'll research it to get the info.