Regional banks Zions Bancorporation ($ZION) and Western Alliance Bancorporation ($WAL) experienced significant drops of 6.4% and 11% respectively due to bad loans and collateral issues. This highlights increasing credit risk in the regional banking sector, following similar write-downs by larger banks like JPMorgan Chase & Co. and Fifth Third Bancorp. Investors should monitor regional banks for further signs of deteriorating loan portfolios.