There is a difference with California legal and Federal legal emission requirements. However if this Ford Explorer is equipped with all the Federal required emission components which it was originally built with (or replaced with OEM parts) it can pass the California smog check and register with the CA DMV as long as its emissions fall below California's exhaust emission limits.
You can use obtain an emissions test in Oregon if you wish and compare the results with California's cut scores for a 1993 Ford Explorer. The Oregon emissions test will not be valid in California but you can use it to see if this Explorer will pass the California smog test.
http://www.smogcheck.ca.gov/pubwebquery/cutpoints/ShowMake.aspx
