Every ZIP code in the United States, with weather, radar, trivia and the numbers behind it. Five digits since 1963!

ZIP stands for Zone Improvement Plan. The codes went live on July 1, 1963.The lowest ZIP code is 00501 — the IRS in Holtsville, New York.The highest ZIP code is 99950, in Ketchikan, Alaska.Type 07734 into a calculator and turn it upside down: hELLO. It is Keansburg, New Jersey.12345 belongs to one company: General Electric in Schenectady, New York.The first digit is a region: 0 is New England and New Jersey, 9 is the West Coast, Alaska and Hawaii.Mr. ZIP, the cartoon mailman, was the mascot that sold the idea to America.ZIP+4 arrived in 1983 and can narrow a ZIP down to one side of one block.A ZIP code is a mail route, not a place: plenty of them cross county and even state lines.Play ZIP Hunt: guess the secret ZIP code of the day in six tries.
zipcodes.pro — ZIP/91310

91310

ZIP 91310 is in Castaic, California, in Los Angeles County; area code 661; Pacific time. Castaic has 2 ZIP codes; the other is 91384.

Type
No street area
Time zone
America/Los_Angeles
County
Los Angeles
Coordinates
34.4889, -118.6229

The Census map gives this ZIP code no delivery area of its own, which usually means it serves post office boxes, a single organization or a post office rather than streets of homes.

This ZIP code has no Census tabulation area of its own. Its point falls inside ZCTA 91384, whose figures describe that area — not this ZIP code.

☼ Live from 91310 — Castaic, CA

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Where 91310 is

This ZIP code has no Census tabulation area, so there is no boundary to draw — the marker is its published point location.

★ Weird and wonderful facts about 91310
  • 🔢 Type 91310 into a pocket calculator and turn it upside down: OIEIG — not quite a word, sorry.
  • ➕ As a number, 91,310 = 2 × 5 × 23 × 397. Its digits add up to 14, a total 1,416 other ZIP codes share.
  • 💾In binary, the way a computer stores it: 10110010010101110
  • 🏠 Its numerical neighbours: 91309 (Canoga Park, CA, 20 mi away) and 91311 (Chatsworth, CA, 14 mi away).
  • 🔄 Backwards, 91310 becomes 01319, which is not a ZIP code at all.
  • 👥 27 other ZIP codes are made of exactly the same digits (01139, 01913, 01931, 03911, 09131, 10913, …). The farthest-flung twin is 09131 in APO AE, a military post office, 5,835 miles away.
  • 🧭 Farther south than 76% of all ZIP codes, and farther west than 92%.
  • 🎯1,161 miles west of the geographic center of the Lower 48, near Lebanon, Kansas.
  • 🌏 Dig straight through the Earth from 91310 and you would come out at 34.49°S, 61.38°E — 1,007 miles from Saint-Denis, Reunion, the nearest big city to that spot.
  • ☀Longest day of the year: 14h 28m of daylight. Shortest: 9h 51m.
🌙 The sky over 91310 today
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🌋 Shake report
  • Checking the USGS…

Source: USGS.

Business and tax activity

Business establishments4This ZIP4
Employees8This ZIP8
Annual payroll$461,000This ZIP$461,000

Land area

ZIP codes near 91310

ZIPCityDistance
91385 Valencia, CA 3.2 mi
91384 Castaic, CA 3.4 mi
91354 Valencia, CA 4.4 mi
91355 Valencia, CA 6.7 mi
91350 Santa Clarita, CA 7.9 mi
91381 Stevenson Ranch, CA 8.0 mi
91380 Santa Clarita, CA 8.1 mi
91382 Santa Clarita, CA 8.1 mi
91383 Santa Clarita, CA 8.1 mi
91322 Newhall, CA 8.9 mi

Find every ZIP code within 10 miles of 91310 →

Questions about this ZIP code

Where is ZIP code 91310?

91310 is in Castaic, California, in Los Angeles County, part of the Los Angeles-Long Beach-Anaheim, CA metropolitan area. Its published point location is 34.4889, -118.6229.

What county is 91310 in?

91310 lies in Los Angeles County.

What area code is 91310?

Castaic uses area code 661, from NANPA's telephone records.

What time zone is 91310 in?

91310 uses America/Los_Angeles.

What ZIP codes are near 91310?

The closest are 91385 (3.2 mi), 91384 (3.4 mi), 91354 (4.4 mi), 91355 (6.7 mi) and 91350 (7.9 mi).

Is 91310 a PO Box ZIP code?

Possibly. The Census map gives this ZIP code no delivery area of its own, which usually means it serves post office boxes, a single organization or a post office rather than streets of homes.

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Cite this page

zipcodes.pro. “91310 ZIP Code — Castaic, California (Los Angeles County).” Data release 2026-10-12. Retrieved 2026-10-20. https://zipcodes.pro/zip/91310

Machine-readable version of these facts:

curl https://zipcodes.pro/zip/91310.json

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