Over the years I've walked most of San Diego's beaches and noticed the lifeguard stations have numbers on them. I've seen them as high as the 20s and 30s. On Mission Beach, just before the jetty there's a number 10. The first tower south of the jetty, in Ocean Beach, is number 6. As you walk south from there, the numbers go as you would expect, from 5 to 1. Where are lifeguard stations 7 through 9?
-- Nancy, on the beach
In the City of San Diego, all of beachdom is divided into three parts: Districts 1, 2, and 3, that is, south, central, and north. Lifeguard towers are numbered in order according to district. For District 1 they reserve tower numbers 1 through 9 (from south to north); District 2, 10 to 29; and District 3, from 30 to whatever. The jetty you speak of is the dividing line between Districts 1 and 2. At the moment, District 1 has only six towers, so the last (most northerly) number in O.B. will be 6. The southernmost tower in District 2 has to be 10. Seven through 9 may exist on some lifeguard service wish list. With this system, if a tower is added or deleted they don't have to renumber every tower, just the ones within a district. And should you ramble as far north as Torrey Pines, all bets are off. That's state beach with a different numbering system.