US citizens along with many other nationalities will be granted a tourist visa upon entry to Colombia.  You can check specific nationalities at

Check-Mig (Migration) form: 
The Colombia Check-Mig is a pre-registration form for entering the country. All passengers crossing the Colombian border must have a completed Colombia Check-Mig. The Colombia Check-Mig was introduced as part of Colombia's COVID-19 travel restrictions. It is still an entry and exit requirement according to the country's immigration policy.
Travelers can complete their Colombia Check-Mig form quickly and easily online. Simply enter your details into the relevant fields and you'll receive the document by email. The process is done 100% online. All you have to do is complete the form using a computer or device connected to the internet. It only takes a matter of minutes to complete. 
This is the link to the Check-Mig form: