Really nice full suspension bike designed by Mike Ahrens (Ahrens Design Group) and built by Paul Sadoff of Rock Lobster.  The bike has had several changes in its life (see story below) and is built with circa 1998 parts or so.  The CODA disc brakes were available in 1998 but the tabs were added to the frame in 2004. 

From Mike Ahrens: "This frame was built for Bret Waters, the owner of KaloMTB, a Bay Area web-based bike shop.  It used to be dark green (photo below) with yellow stickers...original build date was fall 1996 around the same time San Francisco 'Critical Mass' was coming around.  Since 1997, I've designed, and Paul Sadoff has built, close to twenty frames for Bret's shop. Many of them slalom frames and a few dual-suspension bikes including three custom 7005 DH frames. Check out www.ahrensbicycles.com to see pictures of the Storm trooper DH bikes I designed for Bret a few years ago. 

The threaded holes on the drive-side of the swing arm are used for a simple chain tension device similar to the old-style KORE product that bolted onto square chain stays.  The swing arm machined parts are CNC machined from 4130 Cro-moly and the rest of the tube set is a mixture of Tange Prestige and Columbus tubing.  The rear shock is made by Risse, a company I worked at during college to make ends meet.  The shock valving was custom-designed for a 'high leverage ratio' swing arm design...approximately 2.80:1 -- this ratio provided over 5" of true rear wheel travel once the extra air reservoir was added.  The pivot location was nested close to the BB shell in line with the middle ring and slightly forward of the BB centerline.  Overall this frame design was well-received by riders who owned them, especially since they were made from steel and still relatively light when fully built.  Last year (2004) Paul welded on the disc tab, the frame was re-painted white and the rear shock was replaced with a new one from Risse.  It's basically ready to be ridden with more modern componentry!"