Happy infrastructure week! I’ve been lucky enough to work on engineering projects in several ports along the west coast and have always loved learning about them in general.
When we talk about the relative size of companies or institutions, we usually talk about the continuing ideologies or methods that go into sustaining them. When we talk about the relative size of infrastructure, we usually are referring to a specific project and it’s engineering constraints. When we talk about the size of Ports, and their role in a City, we must do both.
Since the first boats hit water, being able to access international and regional trade through Ports has been a reliable source of economic opportunity and activity. While we could dig deep into the history of these and other Ports, as well as their rich and diverse cultural heritages, the simple summary is that Ports exist because most things are heavy in large quantities, large quantities of things make more money, and money buys things.
We can look at three factors when considering Ports over time: the ability of a Port to produce a mechanical advantage for handling goods, the specific types and quantities of goods that Port is handling, and the social and economic environment that produces goods and benefits from handling them.
In contrast to many of the older Ports in the US and Europe, the Ports along the coast of California have had relatively easy access to modern handling capabilities and have been politically stable and allied for the majority of their existence, with each changing hands between various powers only a few times, usually as part of a far-away treaty. California is the closest point in the Continental US to half the world, and maritime technology was advanced enough such that California was capable of receiving massive cargo ships both from abroad and from the already-industrialized US East Coast. All of this is to say that the differences in the historical growth of these Ports can generally be attributed to their proximity to economic resources than to any real cultural, geopolitical, or technological advantage.
Thanks to the gold rush, San Francisco was the largest Port in California for many years, getting a substantially higher volume of ships than Los Angeles or San Diego due to its proximity to gold-mining and railroad-building operations. These two massively profitable industries were in constant need of heavy equipment and manpower. San Francisco grew as California’s industrial center and remains an economic hub to this day.
While San Francisco was enjoying the Pacific spotlight in the latter half of the 19th Century, Los Angeles and San Diego enjoyed the benefits of being earlier stops in the voyages of clipper ships coming from New York to San Francisco via South America.
Comparing San Diego and Los Angeles from a topographical and geological standpoint, San Diego does have a more shapely natural port as you have pointed out. However, the conditions at sea in Los Angeles are not terribly dangerous by comparison, especially considering the shipwrecking power of waters farther North. They are both generally surrounded by mountains or desert, requiring long passages over land to reach other economic hubs.
In the end, the Port of Los Angeles’s advantage over the Port of San Diego has been that the Los Angeles is closer to most places in California and has almost always had access to oil and the economic activity of oil extraction and processing. The oil factor hardly needs explanation, providing a similar extractive cash flow as the gold rush.
Because things are heavy, it’s easier to move them over water than over land. If you were to send something by ship to San Diego, then by horse, train, or truck to your destination, chances are it would end up on passing through Los Angeles anyway. Los Angeles has a distinct mechanical advantage in that it takes less fuel, feed, or calories to get to or from a Port with the same amount of goods. While San Diego was the closest US Port to a number of respectable cities in the US Southwest, the total area served by the Port in Los Angeles is considerably more economically active within a closer proximity to the Port itself.
Regarding the relationship with the US Naval presence in San Diego, it is worth mentioning that the Navy has a presence up and down the West coast, with operational shipyards in Washington and massive shipbuilding facilities previously operated during the 20th century. As far as the Navy’s operations have been concerned since before the 20th century, San Diego’s role as the closest California Port to the East Coast made it a critical first domestic stopping point after weeks away from American waters. Development of naval technologies and our global political needs have concentrated and shifted the Pacific naval presence to larger, more remote (and private!) installations in Hawaii, San Diego, and Washington, all being at the “frontier” of the US’s geometric boundaries in the Pacific, not counting Alaska. Warships need fuel, provisions, and maintenance for voyages, and the further into the world you can load up your warship, the farther it can go. So, the Navy’s presence in San Diego is not so much a cause of the Port’s relatively smaller size as it is a direct result of the same distance factor making it smaller in the first place: things are heavy.
Go spend a day at a maritime museum. It’s always worth it!
This is an incomplete answer, more about why Los Angeles "won" than why San Diego "lost," but it should cover most of your question. I'm drawing heavily from Mike Davis's City of Quartz (1990).
Prior to the 1860s, the economy of the Los Angeles area was ranch-based, supplying beef to Gold Rush miners, but drought and stockraising in the southern Central Valley led to the collapse of the ranchos' prosperity. With property values plummeting, San Francisco-based capital took a foothold in LA, buying up virtually every major rancho by 1868. A new ruling class emerged, and their first project was attracting the Southern Pacific railroad.
Local SP backers led by banker Isaias Hellman and lawyer Henry O'Melveney wanted to, among other goals, establish Los Angeles as the Southern California terminus of transcontinental rail (before San Diego could get it). Southern Pacific's extension to the Los Angeles River initially disappointed the city, especially given the subsidies it was provided, but the completion of Sunset Route from New Orleans (1883) and the arrival of the Santa Fe railroad (1886) led to a massive development boom in the LA area.
Los Angeles became the city in Southern California, and to a degree overshadowed even San Francisco in the minds of contemporary Americans. As the San José Times-Mercury (today the Mercury News) put it:
The average Eastern mind [now] conceives of California as a small tract of country situated in and about Los Angeles.
The two competing railroads now had a strong incentive to draw people to Los Angeles, and so committed heavily to projects like irrigated agriculture, promoting the area's image, and attracting wealthy investors.
The ensuing real estate boom, which lasted from 1886 to 1889, brought 50,000 new residents to a city that had had a population of around 11,000 at the start of the decade. While San Diego, which experienced its own real estate boom, grew at an even faster pace during that decade, it was left to catch up to Los Angeles — in 1890 its population was still only around 16,000.
The value of San Diego Bay as a natural harbor was understood early on, but the San Diego harbor commission struggled with issues like land acquisition and sand deposition from the San Diego River.
LA's harbor was still a major weakness as well, though. Harrison Gray Otis of the LA Times led the "Free Harbor League," a group of emerging Los Angeles elites, in seeking federal support to develop a port at San Pedro (rather than Santa Monica). The ensuing "Free Harbor fight" was won by the San Pedro side, and by the end of the 19th century a breakwater at San Pedro was under construction. With some creative redistricting, San Pedro and adjacent Wilmington were annexed into Los Angeles proper in 1909, and the opening of the Panama Canal in 1914 made the ports at San Pedro and Long Beach important hubs of Pacific–Atlantic trade.
Concerns about water depth and channel width at San Diego, however, kept the Navy from significantly investing in San Diego until 1919. The city did not enjoy the ludicrous influx of capital and influence that drew the railroads, federal funding, and East Coast migrants to Los Angeles.
While San Diego grew modestly, Los Angeles exploded. Otis and his elite allies worked in common interest with the Chamber of Commerce and the railroads to promote Los Angeles in the eastern United States to great success. Davis writes:
Critics (especially San Franciscans) mocked the hubris that declared Los Angeles 'one of the world's great cities in the making', yet within twenty years a Bismarckian municipal will — manifest in both public works and private monopoly — had created the world's biggest manmade port, aqueduct and inter-urban electric railroad system.