A PO BOX number can be less than or more than four digit. For post office boxes, the general rule is that each box has its own ZIP+4 code.
The last four digit is often one of the following:
1. Zero plus the last three digits of the box number (eg. PO BOX 1001, Los Angeles CA 90001-0001).
2. The last four digits of the box number (eg. PO BOX 9991, Twin Peaks CA 92391-9991).
3. If the box number is less than four digits, enough zeros prepended to the front of the box number to produce a four-digit number(eg. PO BOX 1, Shreveport LA 71161-0001).
However, there is no uniform rule, the zip code plus four is for reference only, the ZIP+4 code must be looked up individually for each box in the USPS offical website.
PO BOX 421, SAN MARCOS, CA 92079-0421
PO BOX 422, SAN MARCOS, CA 92079-0422
PO BOX 423, SAN MARCOS, CA 92079-0423
PO BOX 424, SAN MARCOS, CA 92079-0424
PO BOX 425, SAN MARCOS, CA 92079-0425
PO BOX 426, SAN MARCOS, CA 92079-0426
PO BOX 427, SAN MARCOS, CA 92079-0427
PO BOX 428, SAN MARCOS, CA 92079-0428
PO BOX 429, SAN MARCOS, CA 92079-0429
PO BOX 430, SAN MARCOS, CA 92079-0430
PO BOX 431, SAN MARCOS, CA 92079-0431
PO BOX 432, SAN MARCOS, CA 92079-0432
PO BOX 433, SAN MARCOS, CA 92079-0433
PO BOX 434, SAN MARCOS, CA 92079-0434
PO BOX 435, SAN MARCOS, CA 92079-0435
PO BOX 436, SAN MARCOS, CA 92079-0436
PO BOX 437, SAN MARCOS, CA 92079-0437
PO BOX 438, SAN MARCOS, CA 92079-0438
PO BOX 439, SAN MARCOS, CA 92079-0439
PO BOX 440, SAN MARCOS, CA 92079-0440
PO BOX 441, SAN MARCOS, CA 92079-0441
PO BOX 442, SAN MARCOS, CA 92079-0442
PO BOX 443, SAN MARCOS, CA 92079-0443
PO BOX 444, SAN MARCOS, CA 92079-0444
PO BOX 445, SAN MARCOS, CA 92079-0445
PO BOX 446, SAN MARCOS, CA 92079-0446
PO BOX 447, SAN MARCOS, CA 92079-0447
PO BOX 448, SAN MARCOS, CA 92079-0448
PO BOX 449, SAN MARCOS, CA 92079-0449
PO BOX 450, SAN MARCOS, CA 92079-0450
PO BOX 451, SAN MARCOS, CA 92079-0451
PO BOX 452, SAN MARCOS, CA 92079-0452
PO BOX 453, SAN MARCOS, CA 92079-0453
PO BOX 454, SAN MARCOS, CA 92079-0454
PO BOX 455, SAN MARCOS, CA 92079-0455
PO BOX 456, SAN MARCOS, CA 92079-0456
PO BOX 457, SAN MARCOS, CA 92079-0457
PO BOX 458, SAN MARCOS, CA 92079-0458
PO BOX 459, SAN MARCOS, CA 92079-0459
PO BOX 460, SAN MARCOS, CA 92079-0460
PO BOX 461, SAN MARCOS, CA 92079-0461
PO BOX 462, SAN MARCOS, CA 92079-0462
PO BOX 463, SAN MARCOS, CA 92079-0463
PO BOX 464, SAN MARCOS, CA 92079-0464
PO BOX 465, SAN MARCOS, CA 92079-0465
PO BOX 466, SAN MARCOS, CA 92079-0466
PO BOX 467, SAN MARCOS, CA 92079-0467
PO BOX 468, SAN MARCOS, CA 92079-0468
PO BOX 469, SAN MARCOS, CA 92079-0469
PO BOX 470, SAN MARCOS, CA 92079-0470
PO BOX 471, SAN MARCOS, CA 92079-0471
PO BOX 472, SAN MARCOS, CA 92079-0472
PO BOX 473, SAN MARCOS, CA 92079-0473
PO BOX 474, SAN MARCOS, CA 92079-0474
PO BOX 475, SAN MARCOS, CA 92079-0475
PO BOX 476, SAN MARCOS, CA 92079-0476
PO BOX 477, SAN MARCOS, CA 92079-0477
PO BOX 478, SAN MARCOS, CA 92079-0478
PO BOX 479, SAN MARCOS, CA 92079-0479
PO BOX 480, SAN MARCOS, CA 92079-0480
PO BOX 481, SAN MARCOS, CA 92079-0481
PO BOX 482, SAN MARCOS, CA 92079-0482
PO BOX 483, SAN MARCOS, CA 92079-0483
PO BOX 484, SAN MARCOS, CA 92079-0484
PO BOX 485, SAN MARCOS, CA 92079-0485
PO BOX 486, SAN MARCOS, CA 92079-0486
PO BOX 487, SAN MARCOS, CA 92079-0487
PO BOX 488, SAN MARCOS, CA 92079-0488
PO BOX 489, SAN MARCOS, CA 92079-0489
PO BOX 490, SAN MARCOS, CA 92079-0490
PO BOX 491, SAN MARCOS, CA 92079-0491
PO BOX 492, SAN MARCOS, CA 92079-0492
PO BOX 493, SAN MARCOS, CA 92079-0493
PO BOX 494, SAN MARCOS, CA 92079-0494
PO BOX 495, SAN MARCOS, CA 92079-0495
PO BOX 496, SAN MARCOS, CA 92079-0496
PO BOX 497, SAN MARCOS, CA 92079-0497
PO BOX 498, SAN MARCOS, CA 92079-0498
PO BOX 499, SAN MARCOS, CA 92079-0499
PO BOX 500, SAN MARCOS, CA 92079-0500
PO BOX 501, SAN MARCOS, CA 92079-0501
PO BOX 502, SAN MARCOS, CA 92079-0502
PO BOX 503, SAN MARCOS, CA 92079-0503
PO BOX 504, SAN MARCOS, CA 92079-0504
PO BOX 505, SAN MARCOS, CA 92079-0505
PO BOX 506, SAN MARCOS, CA 92079-0506
PO BOX 507, SAN MARCOS, CA 92079-0507
PO BOX 508, SAN MARCOS, CA 92079-0508
PO BOX 509, SAN MARCOS, CA 92079-0509
PO BOX 510, SAN MARCOS, CA 92079-0510
PO BOX 511, SAN MARCOS, CA 92079-0511
PO BOX 512, SAN MARCOS, CA 92079-0512
PO BOX 513, SAN MARCOS, CA 92079-0513
PO BOX 514, SAN MARCOS, CA 92079-0514
PO BOX 515, SAN MARCOS, CA 92079-0515
PO BOX 516, SAN MARCOS, CA 92079-0516
PO BOX 517, SAN MARCOS, CA 92079-0517
PO BOX 518, SAN MARCOS, CA 92079-0518
PO BOX 519, SAN MARCOS, CA 92079-0519
PO BOX 520, SAN MARCOS, CA 92079-0520
PO BOX 521, SAN MARCOS, CA 92079-0521
PO BOX 522, SAN MARCOS, CA 92079-0522
PO BOX 523, SAN MARCOS, CA 92079-0523
PO BOX 524, SAN MARCOS, CA 92079-0524
PO BOX 525, SAN MARCOS, CA 92079-0525
PO BOX 526, SAN MARCOS, CA 92079-0526
PO BOX 527, SAN MARCOS, CA 92079-0527
PO BOX 528, SAN MARCOS, CA 92079-0528
PO BOX 529, SAN MARCOS, CA 92079-0529
PO BOX 530, SAN MARCOS, CA 92079-0530
PO BOX 531, SAN MARCOS, CA 92079-0531
PO BOX 532, SAN MARCOS, CA 92079-0532
PO BOX 533, SAN MARCOS, CA 92079-0533
PO BOX 534, SAN MARCOS, CA 92079-0534
PO BOX 535, SAN MARCOS, CA 92079-0535
PO BOX 536, SAN MARCOS, CA 92079-0536
PO BOX 537, SAN MARCOS, CA 92079-0537
PO BOX 538, SAN MARCOS, CA 92079-0538
PO BOX 539, SAN MARCOS, CA 92079-0539
PO BOX 540, SAN MARCOS, CA 92079-0540
PO BOX 541, SAN MARCOS, CA 92079-0541
PO BOX 542, SAN MARCOS, CA 92079-0542
PO BOX 543, SAN MARCOS, CA 92079-0543
PO BOX 544, SAN MARCOS, CA 92079-0544
PO BOX 545, SAN MARCOS, CA 92079-0545
PO BOX 546, SAN MARCOS, CA 92079-0546
PO BOX 547, SAN MARCOS, CA 92079-0547
PO BOX 548, SAN MARCOS, CA 92079-0548
PO BOX 549, SAN MARCOS, CA 92079-0549
PO BOX 550, SAN MARCOS, CA 92079-0550
PO BOX 551, SAN MARCOS, CA 92079-0551
PO BOX 552, SAN MARCOS, CA 92079-0552
PO BOX 553, SAN MARCOS, CA 92079-0553
PO BOX 554, SAN MARCOS, CA 92079-0554
PO BOX 555, SAN MARCOS, CA 92079-0555
PO BOX 556, SAN MARCOS, CA 92079-0556
PO BOX 557, SAN MARCOS, CA 92079-0557
PO BOX 558, SAN MARCOS, CA 92079-0558
PO BOX 559, SAN MARCOS, CA 92079-0559
PO BOX 560, SAN MARCOS, CA 92079-0560
PO BOX 561, SAN MARCOS, CA 92079-0561
PO BOX 562, SAN MARCOS, CA 92079-0562
PO BOX 563, SAN MARCOS, CA 92079-0563
PO BOX 564, SAN MARCOS, CA 92079-0564
PO BOX 565, SAN MARCOS, CA 92079-0565
PO BOX 566, SAN MARCOS, CA 92079-0566
PO BOX 567, SAN MARCOS, CA 92079-0567
PO BOX 568, SAN MARCOS, CA 92079-0568
PO BOX 569, SAN MARCOS, CA 92079-0569
PO BOX 570, SAN MARCOS, CA 92079-0570
PO BOX 571, SAN MARCOS, CA 92079-0571
PO BOX 572, SAN MARCOS, CA 92079-0572
PO BOX 573, SAN MARCOS, CA 92079-0573
PO BOX 574, SAN MARCOS, CA 92079-0574
PO BOX 575, SAN MARCOS, CA 92079-0575
PO BOX 576, SAN MARCOS, CA 92079-0576
PO BOX 577, SAN MARCOS, CA 92079-0577
PO BOX 578, SAN MARCOS, CA 92079-0578
PO BOX 579, SAN MARCOS, CA 92079-0579
PO BOX 580, SAN MARCOS, CA 92079-0580
PO BOX 581, SAN MARCOS, CA 92079-0581
PO BOX 582, SAN MARCOS, CA 92079-0582
PO BOX 583, SAN MARCOS, CA 92079-0583
PO BOX 584, SAN MARCOS, CA 92079-0584
PO BOX 585, SAN MARCOS, CA 92079-0585
PO BOX 586, SAN MARCOS, CA 92079-0586
PO BOX 587, SAN MARCOS, CA 92079-0587
PO BOX 588, SAN MARCOS, CA 92079-0588
PO BOX 589, SAN MARCOS, CA 92079-0589
PO BOX 590, SAN MARCOS, CA 92079-0590
PO BOX 591, SAN MARCOS, CA 92079-0591
PO BOX 592, SAN MARCOS, CA 92079-0592
PO BOX 593, SAN MARCOS, CA 92079-0593
PO BOX 594, SAN MARCOS, CA 92079-0594
PO BOX 595, SAN MARCOS, CA 92079-0595
PO BOX 596, SAN MARCOS, CA 92079-0596
PO BOX 597, SAN MARCOS, CA 92079-0597
PO BOX 598, SAN MARCOS, CA 92079-0598
PO BOX 599, SAN MARCOS, CA 92079-0599
PO BOX 600, SAN MARCOS, CA 92079-0600
PO BOX 601, SAN MARCOS, CA 92079-0601
PO BOX 602, SAN MARCOS, CA 92079-0602
PO BOX 603, SAN MARCOS, CA 92079-0603
PO BOX 604, SAN MARCOS, CA 92079-0604
PO BOX 605, SAN MARCOS, CA 92079-0605
PO BOX 606, SAN MARCOS, CA 92079-0606
PO BOX 607, SAN MARCOS, CA 92079-0607
PO BOX 608, SAN MARCOS, CA 92079-0608
PO BOX 609, SAN MARCOS, CA 92079-0609
PO BOX 610, SAN MARCOS, CA 92079-0610
PO BOX 611, SAN MARCOS, CA 92079-0611
PO BOX 612, SAN MARCOS, CA 92079-0612
PO BOX 613, SAN MARCOS, CA 92079-0613
PO BOX 614, SAN MARCOS, CA 92079-0614
PO BOX 615, SAN MARCOS, CA 92079-0615
PO BOX 616, SAN MARCOS, CA 92079-0616
PO BOX 617, SAN MARCOS, CA 92079-0617
PO BOX 618, SAN MARCOS, CA 92079-0618
PO BOX 619, SAN MARCOS, CA 92079-0619
PO BOX 620, SAN MARCOS, CA 92079-0620
PO BOX 621, SAN MARCOS, CA 92079-0621
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