From phoneinfosite.com:

Area code 435 is in Utah (Logan, St. George, Moab and all of Utah excluding Salt Lake City, Ogden, Provo and central Utah).


Exchange 435-603
Exchange 603 is in or around West valley city, UT. (Salt lake County, Zipcode 84119)

From Yellow.com:

Phone Company Information Found

Location   County   Provider                                  Phone Type

Hyrum, UT  Cache   Teleport Communications Group, Inc. - Ut   LandLine