Riverside County and San Bernardino County to the north form this metro area. Like many such metro areas in the Southwest, it extends far into uninhabited desert areas, in this case east through the Mojave Desert to the Nevada/Arizona border. Larger than nine U.S. states, it is often referred to as the Inland Empire.
I agree with tchrist that the word doctor in doctor appointment is a noun (attributive noun I believe), although the definition of an attributive noun is a noun used as an adjective, so maybe it's just semantics at some point.
In English, nouns can become adjectives simply by placing them before another noun. They are then adjectivals.. So telephone conversation is fine. Some words have adjective forms that are used, so there are exceptions, but typically, it is simply the placement that makes them function as adjectives. The list is legion: book club, watch band, love match, etc. etc. etc.