You'll actually need to file both California and Colorado tax forms at the end of the year. The CA form should only have CA sourced income (your property only). That should've included all of your rental income in the past as well for the entire duration of renting out the property. You'll likely get a refund of a portion of the $10k.
On your CO return, since it is your state of residency, you'll include ALL of your income, regardless of source. You should have a section for "taxes paid to other states," so you're not double-taxed on your property though.
Source: Former Military Volunteer Income Tax Program Coordinator.
Also, if you're looking for another rental, have you considered doing a 1031 exchange? It might be too late now, but it might not.