You will want to determine which level of certification your company will want; building, simple bridge, major bridge( I assume you are a fabricator). They also have certifications for erectors.  Then there are additional "endorsements" to add to those; fracture critical, special paint endorsement.
If you don't have any paint facilities or painters, you won't need to bother going after that, but being in CA you may want to consider the fracture critical, but you don't have to have it.
You will nedd to have specific aspects of how your company operates in written procedures, submitted to AISC/QMC for a document audit that they do in Chicago, before anyone walks into your facility.
BTW, QMC= Quality Management Company is owned by AISC,=American Institute of Steel Construction, and both are out of Chicago, in fact I belive they are in the same building, just different floors.  QMC will do the audit, and either recommend or not recommend to AISC that you met the requirements to be certified or not.
Now, QMC sub contracts out the auditing to the auditiors.  SOme auditiors only work for QMC, others do audits for both QMC and others such as ISO.
This should get you started, I just had my Major Bridge audit two weeks ago, its still fresh in my memory (and yes we passed).
Chris