I am trying to identify what data is stored in each one of these tables. I can see all the fields that are available using the Marketo admin field management panel but it doesn't tell me where those fields reside. Here is diagram of the core entities and their relationships.
You can see the fields that are mapped to your CRM's primary objects (Lead, Contact, Account) by exporting the field map in Admin | Field Management. The Program fields are Marketo only fields, which you won't see in Field Management, but there are only a few of those that you can identify by looking at the Change Program Status and Member of Program filter constraints. The Opportunity fields you can identify by looking at the Has Opportunity and Added to Opportunity filter constraints or in your CRM identify which of the Opportunity object fields are visible to the Marketo sync user. The activities in the Activity Log only have a few fields, which again you can identify by looking at the various filters in the Lead History folder in the Smart List tab of a smart list or smart campaign.