The first medical clinic in Greater Sacramento to house competing health systems opened its doors Monday. Both UC Davis Health System and Catholic Healthcare West share office space in the new Rocklin clinic, dubbed the Placer Center for Health. The systems share a pharmacy, blood-draw station and imaging services. The idea was to use the clinic as an anchor to spur additional growth in southern Placer County. Both health systems had plans for hospitals and medical buildings near the clinic. But the housing bust and high office vacancies have put those plans on hold. Catholic Healthcare West began seeing patients at the new clinic Monday. UC Davis will start seeing patients Sept. 29.