Can US citizens extend their visa for Sri Lanka beyond 30 days?

Yes. For US visitors, who wish to stay more than 30 days in Sri Lanka, it is possible to extend the visa up to a maximum of 90 days after arrival in Sri Lanka.

Sri Lanka visa extensions can be applied at the Department of Immigration and Emigration in Battaramulla, Colombo. US foreign nationals seeking an extension of their tourist ETA should apply for extensions before the expiry of the ETA.