1912 to present

When Arizona became a state, on Valentine's Day, Feb. 14, 1912, four different flags had flown over Tucson: Spanish, Mexican, United States, Confederate, and now the state of Arizona.

1912 to 1940

From 1912-1940, Tucson continued its steady - if not spectacular - growth from a town of about 14,000 (1910 census). Services such as water, electricity, gas, paved streets and public transportation boosted the community's quality of life. The automobile and electric streetcar expanded residential neighborhoods outside the business district. The appearance of the town changed as brick and substantial, multistory stone buildings replaced low, flat-roofed adobe buildings.

The look of Sentinel Peak changed also as students from the University of Arizona in 1916 painted a 70- by 160-foot "A" on the hillside, thereby christening "A" Mountain.

During World War I in 1917 and 1918, Tucsonans weathered vigorous efforts to increase production of vital war materials such as copper, and supported conservation activities like food-savings programs.

Adding to the stress, there was concern about the possibility of Germany invading Arizona through Mexico, severe labor-relations confrontations involving the pacifist union, Industrial Workers of the World (affecting copper mining), and the onset toward the end of the war of the great influenza epidemic.

Foreshadowing Tucson's long aviation history, in 1919 the first municipally owned airport in the United States opened on land that is now the site of the Tucson Rodeo Grounds. Later, in 1927, the airport was moved to the current site of Davis-Monthan Air Force Base and dedicated by famed aviator Charles Lindbergh.

Tucson was the largest city in Arizona until 1920, when the population of Phoenix at 29,050 exceeded Tucson's 20,300.

Prosperous 1920s

The 1920s were mostly prosperous for Tucson. Civic leaders continued to improve the city's social, educational, cultural and economic institutions. The Tucson Museum of Art and the Tucson Symphony were founded.

The Tucson Sunshine Climate Club promoted tourism, selling Tucson's spectacular climate, weather and Old West attributes. In doing so, the club coined the "Old Pueblo" moniker for Tucson and repeated it so often in advertising that the name stuck.

Dude ranches, fine hotels and medical clinics proliferated. Tucson's first two skyscrapers, the Pioneer Hotel and the Consolidated Bank Building, were completed in 1929.

Then the stock market crashed.

The Great Depression of the 1930s affected Tucson dramatically. Construction, farming and mining jobs disappeared. Businesses and banks failed. It was hard for Tucsonans to support their families. The federal government's Works Progress Administration provided much-needed jobs building a dam in Sabino Canyon and the Mount Lemmon Highway.

The 1930s also saw the end of irrigation farming along the Santa Cruz and Rillito rivers. After centuries of perennial flow, increased water usage and groundwater pumping since the 1890s had dried up both the aboveground and underground river flows.

Tucson received national notoriety in 1934 when the famous outlaw John Dillinger and his gang were captured after fleeing from a fire in the downtown Hotel Congress.

Toward the end of the 1930s, business began to recover and new jobs were created. Tucsonans experienced gasoline-powered buses, air conditioning and the first shopping center, at Broadway Village.

By 1940, the population of Tucson had grown to more than 35,000 - about two-thirds Anglo and one-third Hispanic, mostly of Mexican heritage.

1940 to present

In 1940 Tucson began to increase pumping of groundwater, the growing city's only water source for decades to come. The amount of water taken out of the aquifer exceeded what nature could replace (recharge from rain and snowmelt). By the 1980s, the water table had dropped more than 200 feet in some places and in some areas land had sunk, drawing water away from riparian areas.

Tucson had a major role in training during World War II (1941-1945). Davis-Monthan field became a U.S. Army Air Base. Thousands of pilots were trained there, at Ryan Field west of town and at Marana Air Base to the north. Marana Air Base, activated in 1942, trained 10,000 pilots by the end of the war, becoming the largest pilot-training center in the world.

Infantry and cavalry detachments also were stationed in or near Tucson, training for desert warfare in Africa and testing military equipment.

In 1943, Consolidated Vultee Aircraft (later the Convair division of General Dynamics) built three large hangars at Marana Air Base for B-24 Liberator modifications.

In the late 1940s, Tucson's municipal airport was moved from Davis-Monthan field to its current location, eventually becoming Tucson International Airport. The Army Air Base became Davis-Monthan Air Force Base, and as its military role expanded, emerged as one of Tucson's largest employers.

One of the base's missions - long-term storage of military aircraft - is unique to Tucson, because of our dry climate and alkaline soil. Starting in 1945, out-of-service aircraft have been lined up in the desert "boneyard," awaiting possible return to operational status or providing spare parts. Approximately 4,200 aircraft are stored there today.

1950 to present

Tucson experienced tremendous growth in the 1950s. The population increased fourfold, from 55,000 in 1950 to almost 213,000 in 1960.

Reasons for the huge growth rate included increased manufacturing, with new industries moving to Tucson, a huge increase in tourism leading to a construction boom, the permanent return of servicemen who were trained in Tucson during World War II, and even the wide use of air conditioning that made desert life much more pleasant year-round.

One of the keystone industry startups during this period was Hughes Aircraft Co., which in 1951 built a new manufacturing plant next to the Tucson airport. After initially manufacturing radar units, the company gradually transitioned to producing military missiles, becoming the premier missile builder in the U.S. Today as Raytheon Missile Systems, it is Tucson's second-largest employer.

The 1960s in Tucson started with a business slowdown, but the population still expanded rapidly because of a tidal wave of immigration. The percentage of Anglos in Tucson, which had been increasing for years, peaked near 80 percent but began to decline as the percentage of Hispanics increased - a trend continuing to this day.

Mid-60s growth spurt

Business began to pick up by the mid-1960s. The big copper mines that ringed the town expanded and stepped up production. Nearby enterprises such as Titan missile sites and the astronomical observatory at Kitt Peak added to Tucson's economy.

Construction of the I-10 and I-19 freeways started in the '60s and was completed in the 1970s. New industries came to town, including International Business Machines in 1978.

Meanwhile, another critical Tucson problem - the water supply - was being addressed. Over 20 years, starting in 1973, the Central Arizona Project built a 336-mile diversion canal from the Colorado River to Tucson and in 1992 started providing water to Tucsonans to supplement the limited groundwater.

After resolving some CAP water-quality problems, in 2001 Tucson began blending CAP water and underground water. In an effort to conserve water, today Tucson is recharging groundwater with some of the CAP water.

Tucsonans began historic preservation efforts. Designation of historic neighborhoods began in 1976 and continues today. In 1999, voters approved the Tucson Origins Heritage Park project to begin partial restoration and interpretation of the Tucson Presidio and San Agustín de Tucson Mission Gardens.

In the 2000s, a 2 1/2-mile historical walking tour of downtown Tucson - The Presidio Trail - was completed.

The UA and technology

As Tucson entered the 21st century, the University of Arizona led an advanced-technology business revolution in Tucson with numerous lunar and planetary spacecraft and astronomy programs that make the UA the region's largest employer today. Roughly 150 Tucson companies are involved in the design and manufacture of optics and optoelectronics systems.

Another emerging high-tech industry in Tucson is biosciences, including hospitals, medical-device firms and drug-research companies. Tucson has become well known for its care of heart and cancer patients and its responsive trauma centers.

Recreation was not neglected in Tucson. Rillito River Park, 500 miles of metro bicycle paths, 300 miles of mountain biking trails, more than 120 parks (including Saguaro National Park), and dozens of golf courses and mountain hiking trails attract residents and visitors. Tourism is now a $2 billion a year business with 3.5 million visitors annually.

Four casinos in the Tucson area - owned and operated by Native Americans - provide gaming opportunities. Annual events such as El Tour de Tucson, the Gem and Mineral Show and the Tucson Rodeo are nationally known and widely attended.

The city of Tucson's population was just more than 520,000 at the 2010 census, with the growth rate slowing. The proportion of Hispanics (41.6 percent) compared to Anglos (47.2 percent) continues to grow. More people are settling outside the city as the 2010 population of metropolitan Tucson approached 1 million people.

Facing the future

Tucson faces serious problems. Since the 1970s there has been steady growth in smuggling of illegal drugs from Mexico. Illegal immigration across the Mexican border started to increase dramatically in the 1990s. For years, Tucson's downtown has been in urgent need of urban renewal and planning for business development. These issues persist.

Other issues confronting Tucson today include public transportation and deteriorating roadways. Environmentalists are upset about proposed new mining near Tucson. And water conservation - saving what Tucson has and providing for the future - remains perhaps the city's greatest challenge.

Will Tucson's allocation of CAP water from the Colorado River support continued Tucson growth? And more basic perhaps, will the Colorado River continue to provide enough water to satisfy all its many customers in the Southwestern United States?

Tucsonans have always faced challenges, from 11,000 years ago as wandering hunter-gatherers, through the last 4,000 years or so in permanent settlements along the Santa Cruz River, as perhaps the longest continuous human presence anywhere in the U.S. That impressive history offers hope for a bright, if uncertain, future.

About this series

This is the last in a six-part series on the history of Tucson. In this series, author Bob Ring is writing about the major events that shaped Tucson's development.

Read the other parts of the series at azstarnet.com/bobring online.

• Part 1: Tucson's first residents: Hunter-gatherers to farmers

• Part 2: The Hohokam and later people

• Part 3: Spanish missionaries

• Part 4: The Spanish/Mexican presidio

• Part 5: Tucson in U.S. territory

• Part 6 (today): Tucson in the state of Arizona

E-mail Bob Ring at ringbob1@aol.com

Sources: "Arizona: A Cavalcade of History" (Marshall Trimble, 1989); "Arizona: A Celebration of the Grand Canyon State" (Jim Turner, 2011); "Arizona: A History" (Thomas E. Sheridan, 2012); "Historical Atlas of Arizona" (Henry Walker and Don Bufkin, 1979); "Images of America: Early Tucson" (Anne I. Woosley, 2008); "Tucson: The Life and Times of an American City" (C.L. Sonnichsen, 1982).