Apparently I need an engineer's signoff?

Working on a ground mounted system on my property and I have a full set of plans, but the generic engineering letter from IronRidge isn't sufficient.

The AHJ said "Please provide site specific foundation plans and structural calculations for the proposed ground-mounted photovoltaic structure signed and stamped by a CA Registered Design Professional (i.e. Engineer or Architect)."

Does anyone have a recommendation for how to get this done in California? Like, who?