The powers provided herein for instruction of the third and fourth year college curriculum shall be exercisable only by community college districts which at the date of the filing of notice of establishment of upper divisions as required are urban area districts, which is defined as a taxing district containing: (a) market value for assessment purposes of taxable property of not less than three hundred fifty million dollars ($350,000,000); and (b) a population of not less than ninety thousand (90,000) persons, in the taxing district where the college is located.