Mexico

It was discovered in 1542 and was integrated into the territories of the Viceroyalty of the New Spain (as Mexico was formerly known when it was a colony of Spain). When Mexico won its war of independence against Spain in 1821, California also became part of Mexico on that date and continued to be a territory of Mexico until the Mexican-American War. At the end of such conflict in 1848, the Treaty of Guadalupe-Hidalgo ceded such territories to the US.

So, you can say California belonged to the entity that eventually became Mexico for 306 years since its discovery until its cession, or you can say it belonged to the modern country of Mexico for only 27 years.

You mean the coastal city with the largest population? That would be Tijuana, on the Baja California Peninsula. It has a population of 1,751,302 people, and it is the 7th most populated city in Mexico.

The "beach" you are referring to would be Playasde Tijuana, spanning from the US-Mexico border down to Rosarito, 28 kilometers (17 miles) due south.

Some mountains and lakes in Mexico would be:

• Pico de Orizaba Volcano - 5,636 meters (18,490 ft) - tallest in the country
• Popocatepetl Volcano - 5,426 meters (17,802 ft)

• Chapala Lake - 1261 sq km (487 sq mi)
• La Angostura Reservoir - 640 sq km (247 sq mi)
• Miguel Aleman Reservoir - 500 sq km (193 sq mi)

American presidents John Tyler (term 1841-1845) and James K. Polk (term 1845-1849) had a crush for California and looked to acquire it by any means necessary. The immediate consequences of such actions led to the Mexican Cession, where the United States acquired by force the states of California, Nevada, Utah, Texas and parts of Colorado, Arizona, New Mexico, and Wyoming. Ultimately, this led to the American Civil War(1861-1865).

Causes:

When Mexico won its independence from Spain in 1821, all the territories it possessed included Mexico, most of Central America (Belize, Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica and Panama) as well as today's US States of California, Nevada, Utah, Texas and parts of Colorado, Arizona, New Mexico, and Wyoming.

Due to the extremely low population for such territorial extension (estimated at 12 million during 1824), Mexico relaxed its immigration policies, thus allowing American settlers to help populate the northern territories. The conditions to settle were simple: 1) to pledge allegiance to Mexico and 2) observe the Mexican Law and customs. In 1830, these laws incorporated the banning of slavery. Due to the fact that many American settlers in such territories were slave owners, they looked for any pretext to break up with Mexico.

Later, Mexican President Antonio Lopez de Santa Anna took measures to transform Mexico from a Federal Republic to a Centralist Republic. This move prompted Yucatan and Texas to secede from Mexico. Santa Anna's government invaded both republics; while Yucatan was regained, Texas was lost. As it happens to be the case between today's mainland China and Taiwan, Mexico looked Texas as a rebellious province to be reincorporated at a later time, preferably by diplomatic means, but by force if necessary. The Mexican government warned America that annexation would mean war.

Then, American President John Tyler found out about California and its riches. On a letter by American Plenipotentiary Minister in Mexico, Waddy Thompson, Jr.:

"As to Texas I regard it as of very little value compared with California, the richest, the most beautiful and the healthiest country in the world... with the acquisition of Upper California we should have the same ascendency on the Pacific... France and England both have had their eyes upon it."

He then desperately looked to fulfill the Manifest Destiny, a term which called for the annexation of all North America into the United States. He didn't believed in Texas but looked to annex all the territories west of the Louisiana, being California the "Jewel of the Crown". Long story short, he pushed for annexation of Texas, offering its admission to the Union in March 1, 1845. Then, President James K. Polk ratified by law such admission, on December 29 of that year. These events led to the war with Mexico.

Consequences:

Mexico lost the war due to poor strategic decisions and numeric and technological superiority by American forces: almost 79,000 American soldiers against an army of up to 40,000 Mexican regulars. The Treaty of Guadalupe Hidalgo (Tratado de Guadalupe Hidalgo in Spanish) is the peace treaty, largely dictated by the United States to the interim government of a militarily occupied Mexico, that ended the war. The cession that the Treaty facilitated included parts of the modern-day US states of Colorado, Arizona, New Mexico, and Wyoming, as well as the whole of California, Nevada, and Utah, and, depending on one's point of view, Texas.

As much of this conflict was instigated by Texas and its slave owners (when Texas seceded from Mexico, former American settlers regained their "right" to purchase and sell slaves), this meant an increase in slave territory. In 1849, General Zachary Taylor became President after keeping views on slavery in Texas secret during his campaign. He then revealed his plan to admit California and New Mexico as free states excluding creation of territories subject to slavery. Texas, supported by the other slave states, threatened military action to enforce its claim to New Mexico land, thus setting the stage for the American Civil War (1861-1865).