MONTEREY BAY boundaries
and county lines for birding offshore in Monterey & Santa Cruz counties
a discussion by Don Roberson

To understand the boundaries that birders use as county lines offshore, it helps to understand the concepts of sovereignty (a nation's supreme power within its borders) and jurisdiction (right of a legal or political agency to exercise its authority over a person, subject matter, or territory). In the United States there are four distinct zones to which jurisdiction (in a formal legal sense) applies:

  • The FIRST ZONE is for formal county jurisdiction (e.g., the county sheriff can arrest you). In California, these county boundaries are described in excruciating detail in the California Government Code, including any islands offshore that are within that county. All coastal counties include a portion of the Pacific Ocean out to three nautical miles [or more when a "closed bay" is involved, see below].
  • The SECOND ZONE is official state jurisdiction (e.g., Calif. Fish & Game officers can arrest you). Because the State of California exercises its authority through the county court system, the borders of California incorporate all the land and offshore waters that are attributed to the 58 counties in the Government Code.
  • The THIRD ZONE is a zone of official United States sovereignty (the FBI can arrest you). Under international law this is 12 nautical miles from the nearest point of land (including islands; sometimes farther when "closed bays" are involved). Under international law, a nation exercises complete power over this 12 nmi zone and can exclude ships or persons from other nations.
  • The FOURTH ZONE is the zone of internationally recognized jurisdiction — the "Exclusive Economic Zone" or EEZ — over sea-bed and fisheries resources. Although any nation's ship can transit the waters under the doctrine of "freedom of the seas, the nation with EEZ jurisdiction may regulate fishing, seabed mining, oil drilling, etc. This jurisdiction is 200 nautical miles from the nearest point of land, including islands (see footnote 1).

Birding boundaries: on land, birders use the official boundaries of nations, states, and counties — in California, the latter are in the Government Code and appear on all good maps. Offshore, birders use the boundaries of the Exclusive Economic Zone [EEZ] to extend national, state, and county boundaries out to 200 nmi [nautical miles; see footnote 2]. The outer EEZ boundaries appear on many good nautical maps and have been officially adopted by the AOU and SACC, among others. In practice, since the Government Code describes the limits of the first 3 nmi offshore, those limits are applied to county lines near-shore. Beyond the 3-mile-limit, birders worldwide have adopted the "nearest point of land" protocol to determine county limits between 3 nmi to 200 nmi offshore. An excellent map showing these county limits at sea is on Kurt Radamaker's website. This map (right), from that website, shows the county limits at sea as applied to the central coast of California.

Because islands — such as the Farallones — and prominent coastal headlands — Pt. Reyes, Pt. Sur, Pt. Conception — dominate when applying the "nearest point of land" far offshore, some counties have large slices of ocean offshore and others have very small slices. And again, these boundaries on the map at right only reflect the situation between the 3-nmi-limit and 200 nmi limit.

In the Monterey Bay area we rarely get more than 30 miles west of Pt. Pinos, so the bigger problem is determining the county boundaries within Monterey Bay. Let's turn our attention to that topic.

The problem of "closed bays"

The existence of "closed bays" provides an exception to the rule that coastal counties run offshore for 3 nmi. San Francisco Bay is a classic "closed bay." It is a huge bay but very narrow at its mouth to the sea. Today the Golden Gate Bridge crosses close to the narrowest part of San Francisco Bay. All the Bay to the east of the Golden Gate Bridge is divided up between counties in the Government Code. The 3 mile seaward portion of San Francisco and Marin counties runs westward from that narrowest point of the Bay.

Although Monterey Bay is quite different in shape than San Francisco Bay, legally it is a "closed bay." The U.S. Supreme Court determined in U.S. v. California (1965) 381 US 139, 14 L.Ed.2d 296, that Monterey Bay was a "closed bay" under international law. Thus the State of California had jurisdiction well beyond the expected 3-mile limit — not just 3 miles off Moss Landing — to about 12 miles seaward. The narrowest point is a line between Pt. Pinos in Pacific Grove and Lighthouse Pt. in Santa Cruz (the yellow line on the map at left). Then the 3-mile-limit extends 3 nmi west from the narrowest point of the Bay (shown in the paler green-blue on the map).

In fact, the California Supreme Court case of Ocean Indus. v. Superior Court of California, in & for Santa Cruz County (1927) 200 Cal. 235, 252 P. 722, held that the county lines continued across all of Monterey Bay so that the county courts had jurisdiction over claims of illegal fishing anywhere in the Bay.

In that case, fishermen fishing for sardines and anchoring 3.5 miles off the coastline in the Monterey Bay claimed they could not be prosecuted for violation of fishing limits, etc., because the State and the County had no jurisdiction. In a long opinion, citing much international law and going back to the Treaty of Hildalgo, the court held that both the State and the County had jurisdiction over the 'closed bay' between Santa Cruz and Pt. Pinos, plus 3 miles westward into the Pacific Ocean. Thus where Gov't Code sect 23144 read, in defining Monterey County: "Beginning in the Pacific Ocean, at the southwest corner of Santa Cruz; thence east to the mouth of Pajaro River, on the Bay of Monterey; thence up said stream....", the 1927 California Supreme Court case says that spot "in the Pacific Ocean" is 3 miles west of the line between the headlands that enclose Monterey Bay.

This map (left) shows the official county lines across Monterey Bay and to 3 nmi west of the narrowest point of the Bay (footnote 3). The east-west line runs to the mouth of the Pajaro River as it was at the time the statute was enacted. [Today that point is a few hundred yards south of the rip-rap edge of the Pajaro Dunes colony. It does not matter where the actual river mouth is at any particular time, since the river mouth changes seasonally with water flow.]

When we combine the formal county lines set out by law and interpreted by the Supreme Court within Monterey Bay — the red lines on the map below — and then add the principle of "nearest point of land" when seaward of those official boundaries — the yellow line below — we have a complex situation. Fortunately, obtaining a lat-long or GPS location is easily applied against this map of county lines at sea.

A close-up of the map on Radamaker's website (right) illustrates how these lines 'smooth out' as one pulls back from the details.

If you look closely on "google maps" you can see a slight difference in background shading where the official State and county boundaries cross the Bay some 3 miles west of the narrowest part of the Bay and west of the Monterey Peninsula. This shading even shows up on eBird maps.

Unfortunately, eBird maps still apply the "nearest point of land" protocol inside Monterey Bay — more or less as shown by the yellow dotted line on the map at above left, which shows Soquel Canyon. This creates a triangle in Monterey Bay, formed by the official boundary in red and the "nearest point of land" in dots of yellow, that includes most of Soquel Canyon. This location is often visited on pelagic trips but eBird will mistakenly assign birds within that triangle to Santa Cruz Co., when they are actually within the formal boundaries of Monterey County. Except for this problem, eBird works well elsewhere in Monterey Bay and works just fine far offshore.


  1. Treaties between nations can change an offshore boundary to a different spot than "nearest point of land." Further, there have been cases when equitable analysis has moved an offshore line under rules of international law (e.g., North Sea Continental Shelf cases before the Hague International Court or the Anglo-French arbitration of 1977). These cases are rare but have been applied to determine the division of monies for exploitation of seabed resources off the Atlantic states; see Charney, 1981, "The delimitation of lateral seaward boundaries between states in a domestic context," Am. Journal Intern. Law 75: 28-68. None of these concepts affect those of us in coastal central California.
  2. 1 nautical mile = 1.15078 statute mile. Thus the 200 nmi limit is just over 230 statute miles.
  3. Earlier verisions of this web site were before I discovered the 1927 Supreme Court case and misinterpreted the county lines within Monterey Bay. I apologize for that error.
all photos & text © Don Roberson