From Pitkin County Assessor, Mar 26, 2015:

​”Vacant land is taxed at 29% and residential (with a house even if it is a teardown) is taxed at 7.96%. Say a property is valued at $3,000,000 and it is vacant land. You would take the value times 29% which will give you the assessed value and then you multiply it by the mill levy, let’s say it is in the city of Aspen. Here is the formula –

3,000,000 actual value x 29% = $870,000 assessed value x 33.542 mill levy = $29,181.00 taxes due

Now the same property with the house (teardown or not) –

$3,000,000 actual value x 7.96% = $238,800 assessed value x 33.542 mill levy= $8009.82 taxes due.

As you can see there is quite a large difference in the amount of taxes due. The property is classified on January 1 so whatever it is on January 1 is what it is for the entire year. If you have a vacant lot on January 1 it will be taxed at 29%. If there is a house on the property on January 1 it will be taxed at 7.96%.

Remember also that taxes are always paid a year in arrears.”