Conversation so far:
Where was explorer Thomas Mitchell's first expedition?
Thomas Mitchell's first expedition was to the junction of Barwon and Gwydir.
Where did explorer Thomas Mitchell and his party go on their first expedition?
Thomas Mitchell and his party went to the junction of Barwon, and Gwydir on their first expedition.

Question: What was Thomas Mitchell's goal for the first expedition?
Self-contained rewrite: What was explorer Thomas Mitchell's goal for the first expedition?