Thanks for all the help!! We're taking over an existing instance of Marketo/SFDC for a client, so trying to figure out what's happening.
SFDC setting don't show any auto-created opportunities. There is a 'Lead Source' field which is mapped from lead to contact to opportunity. This field was included in the list upload to Marekto so I'm thinking that may auto-create an opportunity when a new contact is created.
Caleb - We are using the convert function. Screen shot below. If that is the cause, is there a way to bypass creating an opportunity? OR a better way to import as contacts? To give you background, these leads have been pre-qualified as part of a paid media effort, which is why we want to sync over as contacts vs. having them sync over as leads.
Thanks again for the help!!