Lycoming, a corruption of the Lenape word for “sandy stream”, originated as a Pennsylvania creek; that state’s Lycoming County was founded around the creek in 1795. How did the name make its way to Diamond Bar? Most likely because of a phone number. From the 1930s to the 1960s, the AT&T monopoly, a.k.a. the Bell System, employed a mnemonic device: the first two digits of your phone number were replaced by their corresponding letters on a telephone dial. Those two letters were then expanded into a catchy word known as a “central office name”. For example, if your phone number was 555-1234, you’d say “KLondike 5-1234”. Here in the eastern SGV, most phone numbers shared the same prefix: 59. Thus they shared the same central office name: “LYcoming”. Landowners Currier and Mildred Thatcher lived on Lycoming Street in 1957, when it was first name-checked in the press. (It was previously called Lemon Road.) My theory is that they named this street and that, since they had no ties to Pennsylvania, they were inspired by their own phone number: LYcoming 2-7777.