Bounties are listed in the timeline now, but not the bounty message. Bounty messages are posted as notices, and moderators can post other notices too.
I've had to remove a bounty from a question today, one with a very verbose notice. That notice was the reason I removed the bounty (it was basically asking a new question), and I'd like to have had that notice preserved for future auditing.
Please add the notice text to the timeline, at least for moderators if not for all users.