Hi Andy
Run Tcode: OADB to configure valuation area and choose non leading ledger to post.
You also can set up depreciation areas for parallel valuation using a wizard Tcode: OADB_WZ
Before you set up valuations area to post in non leading ledger, you should remember that updating the values to CO is possible only for values of the leading ledger, but not for values of the parallel ledger.
Kind Regards
Jandoval Nascimento