Its an area of Class-E airspace used for Instrument Approach Procedures.
From The Pilot Handbook, Chapter 14, Airspace:
Class D airspace is generally airspace from the surface to
2,500 feet above the airport elevation (charted in MSL)
surrounding those airports that have an operational control
tower. The configuration of each Class D airspace area is
individually tailored and when instrument procedures are
published, the airspace is normally designed to contain the
procedures. Arrival extensions for instrument approach
procedures (IAPs) may be Class D or Class E airspace. Unless
otherwise authorized, each aircraft must establish two-way
radio communications with the ATC facility providing air
traffic services prior to entering the airspace and thereafter
maintain those communications while in the airspace.
Also from that handbook, the procedures for operating in Class-E:
If the airspace is not Class A, B, C, or D, and is controlled
airspace, then it is Class E airspace. Class E airspace extends
upward from either the surface or a designated altitude to the overlying or adjacent controlled airspace. When designated
as a surface area, the airspace is configured to contain all
instrument procedures. Also in this class are federal airways,
airspace beginning at either 700 or 1,200 feet above ground
level (AGL) used to transition to and from the terminal or
en route environment, and en route domestic and offshore
airspace areas designated below 18,000 feet MSL. Unless
designated at a lower altitude, Class E airspace begins at
14,500 MSL over the United States, including that airspace
overlying the waters within 12 NM of the coast of the 48
contiguous states and Alaska, up to but not including 18,000
feet MSL, and the airspace above FL 600.
So basically class-E rules apply, but be aware you are operating in an Instrument Approach Procedure area.