Mexico -- United States border - wikipedia Mexico -- United States border This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( December 2014 ) Mexico -- United States border The border between Mexico and the United States spans six Mexican states and four U.S. states. Characteristics Entities Mexico United States Length 1,954 miles ( 3,145 km ) History Current shape December 30, 1853 Treaties Adams -- Onís Treaty, Treaty of Limits ( Mexico -- United States ), Treaty of Guadalupe Hidalgo, Gadsden Purchase Border counties in the United States along the Mexican border To the right lies Tijuana, Baja California, and on the left is San Diego, California. The building in the foreground on the San Diego side is a sewage treatment plant built to clean the Tijuana River. The Mexico -- United States border is an international border separating Mexico and the United States, extending from the Pacific Ocean to the west and Gulf of Mexico to the east. The border traverses a variety of terrains, ranging from major urban areas to uninhabitable deserts. Approximately 350 million legal crossings occur annually, and is the most frequently crossed border in the world. The total length of the continental border is 1,954 miles ( 3,145 km ). From the Gulf of Mexico, it follows the course of the Rio Grande ( Río Bravo del Norte ) to the border crossing at Ciudad Juárez, Chihuahua, and El Paso, Texas. Westward from El Paso -- Juárez, it crosses vast tracts of the Chihuahuan and Sonoran deserts to the Colorado River Delta and San Diego -- Tijuana, before reaching the Pacific Ocean. Contents 1 Geography 1.1 Border region 1.2 Border states 1.3 Border crossing checkpoints 2 History 3 Security 3.1 Background 3.2 Border enforcement 3.3 Border incursions 3.4 Disagreements over need for more resources 3.5 In context of Trump administration 3.5. 1 Proposed wall 3.6 Dangers of border control 4 Border zone policies 4.1 Department of Homeland Security Secure Border Initiative 4.2 100 - mile border zone 4.3 Operation Streamline 4.3. 1 History 4.3. 2 Support and criticisms 5 Environment 5.1 History 5.1. 1 Impacts of Border Wall on Wildlife 6 Travel 6.1 Western Hemisphere Travel Initiative 7 Barrier 8 Veterinary inspections 8.1 Crossing from Mexico to the United States 8.2 Crossing from the United States to Mexico 9 See also 10 References 11 Further reading 12 External links Geography Border region Along this border are 23 U.S. counties and 39 Mexican municipalities, as well as a dramatic population increase. The main factors contributing to population rise are a significant increase in migrations, increase in the number of employment opportunities along the border region in Mexico, and the increase in the number of people illegally crossing the border into the United States in order to find better jobs and living standards. This border also plays a significant role in economic development on both sides and has negative and positive impacts on economic aspects when there is a change in populations or policies. This border also serves as the hub for trade and the exchange of goods. Mutual trade and exchange of goods make both countries depend on each other. Therefore, if one country, for example, faces economic issues, the other will also be affected by a decrease in employment opportunities. Although they may be mutually dependent on trade and economic development, both countries operate on distinct sets on governance, legal, economic, and social systems. This border defines the sovereignty of both countries. Following the Boundary Treaty of 1970 between Mexico and the United States that settled all the pending boundary disputes and uncertainties related to the Rio Grande ( Río Bravo del Norte ) border, the national continental border extends 1,954 miles ( 3,145 km ), excluding the maritime boundaries of 18 miles ( 29 km ) in the Pacific Ocean and 12 miles ( 19 km ) in the Gulf of Mexico. According to the International Boundary and Water Commission, this continental border follows the middle of the Rio Grande -- according to the 1848 Treaty of Guadalupe Hidalgo between the two nations, `` along the deepest channel '' ( also known as the thalweg ) -- from its mouth on the Gulf of Mexico a distance of 1,255 miles ( 2,020 km ) to a point just upstream of El Paso and Ciudad Juárez. It then follows an alignment westward overland and it is marked by monuments for a distance of 534 miles ( 859 km ) to the Colorado River, when it reaches its highest elevation at the intersection with the Continental Divide. It then follows the middle of that river toward the north with a distance of 24 miles ( 39 km ), and ultimately follows an alignment overland toward the west and marked by monuments with a distance of 141 miles ( 227 km ) to the Pacific Ocean. Per the La Paz Agreement, the official `` border area '' ( sometimes called border region ) extends `` 100 kilometers ( 62.5 miles ) on either side of the inland and maritime boundaries '' from the Gulf of Mexico west into the Pacific Ocean. There is also a 100 - mile Border Zone. The region is characterized by deserts, rugged hills, abundant sunshine, and two major rivers -- the Colorado and the Rio Grande ( Río Bravo del Norte ) -- which provide life - giving water to the largely arid but fertile lands along the rivers in both countries. Border Patrol patrolling the Rio Grande in an airboat in Laredo, Texas The start of the border fence in the state of New Mexico -- just west of El Paso, Texas U.S. Border Patrol helicopter along El Camino del Diablo, Arizona -- Sonora border, 2004 Border between Nogales, Arizona, on the left, and Nogales, Sonora, on the right On the left : Nogales, Arizona ; on the right, Nogales, Sonora Beach in Tijuana at the border Border States Vehicle barrier in the New Mexico desert The U.S. states along the border, from west to east, are California, Arizona, New Mexico, and Texas. The Mexican states along the border are Baja California, Sonora, Chihuahua, Coahuila, Nuevo León, and Tamaulipas. Among the U.S. states, Texas has the longest stretch of the border with Mexico, while California has the shortest. Among the states in Mexico, Chihuahua has the longest border with the United States, while Nuevo León has the shortest. Texas borders four Mexican states -- Tamaulipas, Nuevo León, Coahuila, and Chihuahua -- the most of any U.S. states. New Mexico and Arizona each borders two Mexican states ( Chihuahua and Sonora ; Sonora and Baja California, respectively ). California borders only Baja California. Three Mexican states border two U.S. states each : Baja California borders California and Arizona ; Sonora borders Arizona and New Mexico ; and Chihuahua borders New Mexico and Texas. Tamaulipas, Nuevo León, and Coahuila each borders only one U.S. state : Texas. Border crossing Checkpoints For a more comprehensive list, see List of Mexico -- United States border crossings. Climbing the Mexico -- United States barrier fence in Brownsville, Texas The border separating Mexico and the United States is the most frequently crossed international boundary in the world, with approximately 350 million legal crossings taking place annually. There are 48 U.S. -- Mexico border crossings, with 330 ports of entry. At these points of entry, people trying to get into the U.S. are required to open their bags for inspection. Border crossings take place by roads, pedestrian walkways, railroads and ferries. From west to east, below is a list of the border city `` twinnings '' ; cross-border municipalities connected by one or more legal border crossings. San Diego, California ( San Ysidro ) -- Tijuana, Baja California ( San Diego -- Tijuana Metro ) Cross Border Xpress, Otay Mesa, California -- Tijuana International Airport, Baja California Otay Mesa, California -- Tijuana, Baja California Tecate, California -- Tecate, Baja California Calexico, California -- Mexicali, Baja California Andrade, California -- Los Algodones, Baja California San Luis, Arizona -- San Luis Río Colorado, Sonora Lukeville, Arizona -- Sonoyta, Sonora Sasabe, Arizona -- Altar, Sonora Nogales, Arizona -- Nogales, Sonora Naco, Arizona -- Naco, Sonora Douglas, Arizona -- Agua Prieta, Sonora Antelope Wells, New Mexico -- El Berrendo, Chihuahua Columbus, New Mexico -- Palomas, Chihuahua Santa Teresa, New Mexico -- San Jerónimo, Chihuahua El Paso, Texas -- Ciudad Juárez, Chihuahua ( El Paso - Juarez ) Fabens, Texas -- Práxedis G. Guerrero, Chihuahua municipality Fort Hancock, Texas -- El Porvenir, Chihuahua Presidio, Texas -- Ojinaga, Chihuahua Heath Canyon, Texas -- La Linda, Coahuila ( closed ) Del Rio, Texas -- Ciudad Acuña, Coahuila Eagle Pass, Texas -- Piedras Negras, Coahuila Laredo, Texas -- Nuevo Laredo, Tamaulipas Laredo, Texas -- Colombia, Nuevo León Falcon Heights, Texas -- Presa Falcón, Tamaulipas Roma, Texas -- Ciudad Miguel Alemán, Tamaulipas Rio Grande City, Texas -- Ciudad Camargo, Tamaulipas Los Ebanos, Texas -- Gustavo Díaz Ordaz, Tamaulipas Mission, Texas -- Reynosa, Tamaulipas Hidalgo, Texas -- Reynosa, Tamaulipas Pharr, Texas -- Reynosa, Tamaulipas Donna, Texas -- Rio Bravo, Tamaulipas Progreso, Texas -- Nuevo Progreso, Tamaulipas Los Indios, Texas -- Matamoros, Tamaulipas Brownsville, Texas -- Matamoros, Tamaulipas The total population of the borderlands -- defined as those counties and municipios lining the border on either side -- stands at some 12 million people. History See also : Rio Grande border disputes and Adams - Onís Treaty Map of Mexico in 1842 San Diego together with Tijuana creates the bi-national San Diego -- Tijuana metropolitan area. In the mid-16th century, with the discovery of silver, settlers from a various countries and backgrounds began to arrive in the area. This period of sparse settlement included colonizers from different backgrounds. A strong feeling of manifest destiny had arose and began allaying internal political divisions with a sense of inevitable expansion. For example, it was not until after the Mexican -- American War and the fulfillment of Manifest Destiny that the Civil War began in the United States, its most prominent generals on both sides having fought together against Mexico just years earlier. The reason the two countries went to war was that both Mexico and the US wanted Texas and California. The United States wanted Texas for its agricultural production, especially cotton, while California was important due to its direct contact with the Pacific. The area was technically part of the Kingdom of New Spain, but due to the lack of population and the diverse citizenry it had, it did not seem to belong to any country. This period lasted until the early 19th century, at which point the United States bought the lands known as the Louisiana Purchase from France and began to expand steadily ( militarily ) westward in its pursuit of Manifest Destiny. El Paso ( top ) and Ciudad Juárez ( bottom ) seen from earth orbit ; the Rio Grande is the thin line separating the two cities through the middle of the photograph. El Paso and Juarez make up the second largest international metroplex after San Diego and Tijuana. The border itself was not clearly defined and remained so until the Mexican colony became independent from Spain and entered a period of political instability. Mexico attempted to create a buffer zone at the border that would prevent possible invasion from the North. The Mexican government encouraged thousands of their own citizens to settle in the region that is now known as Texas and even offered inexpensive land to settlers from the United States in exchange for populating the area. The influx of people did not provide the defense that Mexico had hoped for and instead Texas declared its independence in 1836, which lasted until 1845 when the U.S. annexed it. The constant conflicts in the Texas region in the mid-19th century eventually led to the Mexican -- American War, which began in 1846 and ended in 1848 with the Treaty of Guadalupe Hidalgo. In the terms of the peace treaty, Mexico lost more than 960,000 square miles ( 2,500,000 km ) of land, 55 % of its territory, including what is today California, Arizona, New Mexico, Utah, Nevada and parts of Colorado, Wyoming, Kansas, and Oklahoma. In addition, all disputes over Texas and the disputed territory between Rio Grande and Rio Nueces were abandoned. Five years later the Gadsden Purchase completed the creation of the current United States -- Mexico border. The purchase was initially to accommodate a planned railway right - of - way. These purchases left approximately 300,000 people living in the once disputed lands, many of whom were Mexican nationals. Following the establishment of the current border a number of towns sprang up along this boundary and many of the Mexican citizens were given free land in the northern regions of Mexico in exchange for returning and repopulating the area. The Treaty of Guadalupe Hidalgo and another treaty in 1884 were the agreements originally responsible for the settlement of the international border, both of which specified that the middle of Rio Grande was the border -- irrespective of any alterations in the channels or banks. The Rio Grande shifted south between 1852 and 1868, with the most radical shift in the river occurring after a flood in 1864. By 1873 the moving river - center border had cut off approximately 600 acres ( 2.4 km ) of Mexican territory in the El Paso - Juarez area, in effect transferring the land to the United States. By a treaty negotiated in 1963, Mexico regained most of this land in what became known as the Chamizal dispute and transferred 264 acres ( 1.07 km ) in return to the United States. Border treaties are jointly administered by the International Boundary and Water Commission ( IBWC ), which was established in 1889 to maintain the border, allocate river waters between the two nations, and provide for flood control and water sanitation. Once viewed as a model of international cooperation, in recent decades the IBWC has been heavily criticized as an institutional anachronism, by - passed by modern social, environmental and political issues. The economic development of the border region on the Mexican side of the border depended largely on its proximity to the United States, due to its remoteness from commercial centers in Mexico. Undocumented labor contributes $395 billion to the economy every year. If undocumented labor in the United States was largely Hispanic, it would have the same sized national economy as Sweden and rank ahead of countries such as Switzerland, Austria and Singapore and be bigger, in terms of GDP. Immigration reform has been a huge theme in U.S. politics, in recent years. While the U.S. is in favor of immigration, the increase in undocumented immigration has given border - crossing a negative image. There are around 11.5 million undocumented workers in the U.S. today, and 87 % of undocumented immigrants have been living in the U.S. for more than 7 years. Basic rules of macroeconomics indicate that as long as there are better opportunities existing in the U.S., immigration and the number of undocumented immigrants will continue to rise. Local economies that develop on the Mexican side capitalize not only on available skills but also on available, usually discarded, materials. Small businesses trade in clothes that are purchased by the pound and cardboard from the United States. Some items, like the used tires found everywhere along the border, are made into certain items that support local economies and define a border. During the years of Mexican President Porfirio Díaz, between 1876 and 1910, the border communities boomed, due mostly to close ties to the United States, and the Mexican government 's support for financial investments from the United States. Railroads were built that connected the northern Mexican states more to the United States than to Mexico and the population grew tremendously. The mining industry also developed, as did the United States ' control of it. By the early 20th century companies from the United States controlled 81 % of the mining industry and had invested five hundred million dollars in the Mexican economy overall, twenty - five percent of it in the border regions. 100 - km border region The Mexican Revolution, caused at least partially by animosity toward foreign ownership of Mexican properties, began in 1910. The Revolution increased the political instability in Mexico, but did not significantly slow United States investment. It did reduce economic development within Mexico, however, and the border regions reflected this. As the infrastructure of communities on the United States side continued to improve, the Mexican side began to fall behind in the construction and maintenance of important transportation networks and systems necessary to municipal development. Security Background Data from the United States Border Patrol Agency 's ( USBP ) 2010 annual report shows that among the total number of illegal border crossings from various countries into the United States, 90 percent were from Mexico alone. In addition, there are more than 6 million undocumented Mexican nationals residing in the United States. The border, with its 1,951 miles ( 3,140 km ) in length, has a very high rate of legal and illegal migrant crossings every year. With such a high rate of people crossing annually to the United States, the country has invested in several distinct security measures. The U.S. Border Patrol is perhaps the most important security measure. In 2010, due to insecurity and instability at the southern border of the U.S. President Barack Obama signed an appropriation bill, which gave the Customs and Border Protection, specifically the Border Patrol, 600 million dollars to implement and improve security. The U.S. government has invested many millions of dollars on border security, although this has not stopped illegal immigrants from entering the United States. Border enforcement See also : Illegal immigration to the United States Border Patrol agents in southern Texas in 2013 While the Border Patrol has changed a lot since its inception in 1924, its primary mission remains unchanged : to detect and prevent the illegal entry of aliens into the United States. Together with other law enforcement officers, the Border Patrol helps maintain borders that work - facilitating the flow of legal immigration and goods while preventing the illegal trafficking of people and contraband. In 2012, Border Patrol agents made over 364,000 arrests of people illegally entering the country. Considerable success has been achieved in restoring integrity and safety to the Southwest border, by putting in place a border - control strategy. These include Operation Gatekeeper in San Diego, CA, Operation Hold the Line in El Paso, TX, Operation Rio Grande in McAllen, TX, Operation Safeguard in Tucson, AZ, and the Arizona Border Control Initiative ( ABCI ) along the Arizona border. The border has the highest number of registered legal crossings of any land border in the world. Over five million cars and trucks travel through the border annually. According to Vulliamy, one in five Mexican nationals will visit or work in the United States at one point in their lifetime. As of 2010, the border is guarded by more than twenty thousand Border Patrol agents, more than at any time in its history. However, they only have `` effective control '' of less than 700 miles ( 1,100 km ) of the 1,954 miles ( 3,145 km ) of total border, with an ability to actually prevent or stop illegal entries along 129 miles ( 208 km ) of that border. The border is paralleled by United States Border Patrol Interior Checkpoints on major roads generally between 25 and 75 miles ( 40 and 121 km ) from the U.S. side of the border, and garitas generally within 50 km of the border on the Mexican side. Drug trafficking tunnel under the U.S. - Mexico border used by the Sinaloa Cartel There are an estimated half a million illegal entries into the United States each year. Border Patrol activity is concentrated around border cities such as San Diego and El Paso which have extensive border fencing. This means that the flow of illegal aliens is diverted into rural mountainous and desert areas, leading to several hundred migrant deaths along the Mexico -- U.S. border of those attempting to cross into the United States from Mexico illegally and vice versa. The Secure Fence Act of 2006 was passed providing for the construction of 700 miles ( 1,100 km ) of high - security fencing. Attempts to complete the construction of the Mexico -- United States barrier have been challenged by the Mexican government and various U.S. -- based organizations. In January 2013, the Government Accountability Office released a report stating that the United States Border Patrol only intercepted sixty - one percent of individuals illegally crossing the border in 2011, which translated to 208,813 individuals not apprehended. 85,827 of the 208,813 would go on to illegally enter the United States, while the rest returned to Mexico and other Central American countries. The report also showed that the number of illegal border crossings has dropped. Statistics from the United States Border Patrol agency on apprehensions in the last 10 years in the border region show that 91 percent of the apprehensions made were illegal border crossings. Similarly, the U.S. Border Patrol ( USBP ) statistics show that 90 percent of the people apprehended along the border were from Mexico. The number of apprehensions along the border with Mexico has dramatically declined from 2001 to 2010 as the United States government increased the number border patrol agents and other facilities along the southwest sectors of the border. According to the Department of Homeland Security, there were about 10,000 agents operating along the border areas in 2004 which was increased to 20,500 agents in 2010. The Department of Homeland Security has also installed new technological equipment at the border including car and air surveillance, surveillance cameras, thermal imaging systems, inspection equipment, and so forth. Illegal border crossing is not the sole cause of illegal immigration to the United States, there are also people from various countries legally entering the United States and overstaying beyond their visa status who are also considered illegal immigrants. In 2010, there were approximately 11 million immigrants living the United States that were not authorized. Of the 11 million, 6.1 million people were from Mexico which accounted for 55 percent of the total unauthorized immigrants. Border incursions Border for pedestrians in Tijuana, Baja California According to the U.S. Border Patrol, in the fiscal year of 2006, there were twenty - nine confirmed border incursions by Mexican government officials, of which seventeen were by armed individuals. Since 1996 there have been 253 incursions by Mexican government officials. In 2014 the U.S. Department of Homeland Security informed California Representative Duncan D. Hunter that since 2004, there have been 300 documented border incursions, which resulted in 131 individuals being detained. The Washington Times has reported that on Sunday, August 3, 2008, Mexican military personnel who crossed into Arizona from Mexico encountered a U.S. Border Patrol agent, whom they held at gunpoint. The soldiers later returned to Mexico, as backup Border Patrol agents came to investigate. Disagreements over need for more resources Proponents of greater spending on the border argue that continuing the buildup is necessary due to increased violence and drug trafficking from Mexico spilling into the United States. However, critics such as the Washington Office on Latin America ( WOLA ) have argued that the diminishing number of border crossings can only be partially attributed to U.S. security measures. Unintentional factors, such as a weakened U.S. economy in the wake of the 2008 financial crisis and increased violence in northern Mexico have made attempting illegal border crossings more risky and less rewarding. In context of Trump administration See also : 2017 Mexico -- United States diplomatic crisis In 2016, Donald Trump, then the Republican presidential nominee in the then forthcoming U.S. election repeatedly stated that he wanted to build a wall along the border, for the purpose of immigration control. He declared that Mexico would be forced to pay for the entire wall. Following his Inauguration on January 20, 2017, on January 25 President Trump signed Executive Order 13767 to enable the building of the wall. Shortly afterwards, the Mexican President stated that Mexico will not pay for the wall. Trump had planned to meet Mexican President Enrique Peña Nieto on January 27 in Washington, D.C. to discuss topics including border security. The meeting was cancelled by Peña Nieto, and shortly after, Trump announced that he intended to impose a 20 % tariff on Mexican goods to effectively pay for the wall. As of the end of 2017, Mexico had not entered into any agreement to pay for any amount of the wall, and no new tariffs on Mexican goods had been considered by the U.S. Congress. Also the U.S. Congress had not appropriated funding for a wall, and no further wall construction has started beyond what was already planned during the Obama administration. On September 20, 2017, California Attorney General Becerra filed a lawsuit alleging that the Trump administration has overstepped its powers in expediting construction of a border wall. Proposed wall Some work on building a wall prototype was started. According to United State Customs and Border Protection agency, four major construction companies will bid for the contract. These companies will first produce prototypes of the wall within a month prior to receiving a full contract. The cost of each prototype is estimated at $400,000 to $500,000, and the Customs and Border Protection agency will have $20 million to use to produce these prototypes. President Trump has asked the Congress to assign $1.6 billion to build the wall this year but Congress has only approved $341 million to maintain the existing wall along the border and yet to approve a budget for the newly proposed wall. The exact cost of the newly proposed wall is not clear yet many experts on the issue predicted that it would cost a lot. There are differing opinions and cost estimates of building the wall. The Trump administration has estimated the cost of the wall at $12 billion, but the Department of Homeland Security estimated the cost at $21.6 billion. According to one report, the proposed wall would cost up to $70 billion, a significant difference. There is also no decision made on the actual structure of the wall but according to the Homeland Security Department, the wall would be between 18 and 30 feet high and as deep as 6 feet underground to deter drug traffickers from building tunnels. Dangers of border control The neutrality of this section is disputed. Relevant discussion may be found on the talk page. Please do not remove this message until conditions to do so are met. ( December 2017 ) As American officials have implemented heavier measures each year in terms of border control in efforts to decrease the number of illegal immigrants crossing over, they have simultaneously contributed to the deaths of thousands. It has been found that typically people who choose to illegally cross the Mexico -- United States border do so because they either have no option to legally or because their options entailed waiting several years for paperwork to process. People make the decision of crossing illegally knowing the danger that lies ahead of them because they are also aware of visa restrictions, which provide citizens of wealthier and more democratic countries with more freedom of movement across international borders. In a world that is full of inequality, it comes as no surprise that people born into poorer countries would want to move to those that are richer and provide more opportunity. Because of this, affluent countries such as America feel the need to enhance visa and border restrictions. However, these efforts have not kept determined migrants out, and instead has raised the death toll to an all - time high. It has been proven that America 's border enforcement largely contributes to the deaths of immigrants each year. From the years of 1994 to 2000, there was a sharp increase of migrant deaths of those trying to gain entry. From 1994 to 2001, there were about 1,700 deaths reported along the Southwest border. This is not including the number of bodies that were not reported, which has undoubtedly increased as border enforcement is heavily concentrated in urban areas and is not as concentrated in areas that are more remote. The most convincing evidence of this is the change in causes of death among those trying to cross the border illegally. From 1995 to 2000, most migrant deaths along the Mexico - California border ( 308 of them ) were caused by `` environmental causes. '' These include causes such as hypothermia from freezing to death over the mountains, dehydration from long periods of travelling without water, or heat stroke after days of struggling through the desert. In that same span of years, there was also an increase of deaths by drowning. Drowning is also a direct consequence of the strategy of border enforcement because migrants decide to travel by water to avoid the painful and exhausting heat of the desert. During these years, deaths from environmental factors and drowning together contributed to 78 % of the total deaths, a percentage that increased sharply from years before. People who are considering traveling across the border illegally are generally aware of the dangers that could be encountered in terms of physical risk, but they remain determined. Of a survey done from December 1999 to May 2000 of 262.989 apprehended migrants returned to Mexico by Border Patrol, 70 % expressed that they had risked their lives somehow during their attempt at crossing the border illegally. Of this same group, 36 % expressed that they had experienced extreme heat or cold and 35 % had suffered from dehydration and lack of food. Border Zone policies Department of Homeland Security Secure border Initiative This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( March 2015 ) A U.S. Army National Guard member working with the U.S. Border Patrol in support of Operation Jump Start, Arizona, July 2006 A National Border Patrol Strategic Plan was first developed in 1994 to deal with the fact that borders were being overrun by illegal immigrants and drug dealers. It was then updated in 2004 and 2012. In 2004 the updated strategy focused on command structures, intelligence and surveillance, enforcement and deployment of U.S. Border Patrol agents to better respond to threats at the border. The strategic planning led to broader policy development for the Department of Homeland Security which led to the Secure Border Initiative ( SBI ) in 2005 to secure U.S. borders and reduce illegal migration. The main components of SBI dealt with staffing concerns, removal capacity, surveillance and tactical infrastructure and interior enforcement. An additional component was `` high consequence enforcement '', which was not the subject of a formal public policy document. There was the allowance, historically, for voluntary returns of individuals apprehended at the border by Border Patrol agents. These voluntary returns, after the SBI of 2005, were limited to three `` high consequence outcomes ''. One `` high consequence outcome '' was formal removal, which meant the individual would be deemed ineligible for a visa for at least five years and subject to criminal charges if caught re-entering illegally. The Immigration and Nationality Act permitted aliens to be formally removed with `` limited judicial processing '' known as expedited removal. The Department of Homeland Security has expanded between 2002 and 2006, expedited removal for `` certain aliens that entered within previous two weeks and were apprehended within 100 miles ( 160 km ) of the border ''. Another `` high consequence outcome '' is the increase in criminal charges. Department of Homeland Security has also worked with the Department of Justice to increase the number of apprehended individuals crossing the border illegally who are charged with criminal offenses. Most of these cases are prosecuted under Operation Streamline. The third `` high consequence outcome '' is known as remote repatriation. This is the return of apprehended Mexicans to remote locations by Border Patrol rather than the nearest Mexican port of entry. 100 - Mile border Zone This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( March 2015 ) Members of the North Carolina Army National Guard monitoring the U.S. - Mexico border in southwest Arizona Regulations establishing the 100 - mile ( 160 km ) zone were adopted by the U.S. Department of Justice as the result of an interpretation of the Immigration and Nationality Act in 1953. Customs and Border Protection 's ( CBP ) officials have authority for stop and search within this 100 miles ( 160 km ) from any external boundary. This allows for CBP officials to enter private property without a warrant within 25 miles ( 40 km ) of the border as well as the operation of checkpoints. The Fourth Amendment of the U.S. Constitution protects against unreasonable search and seizure ; however, according to the government this does not fully apply at borders or border crossings ( also known as ports of entry ). This means that much of the U.S. population is subject to CBP regulations for stop and search. The 100 Mile Border Zone includes two thirds of the population, a majority of the largest cities in the U.S. and several entire states ( namely Connecticut, Delaware, Florida, Hawaii, Maine, Massachusetts, Michigan, New Hampshire, and New Jersey ). There are some limits to CBP officials ability to stop and search. For instance CBP officials are not allowed to pull anyone over without a reasonable suspicion of immigration violation or crime, or search vehicles without warrant or probable cause. The ACLU, however, found that CBP officials routinely ignore or misunderstand the limits of authority, and this is compounded by inadequate training, lack of oversight and failure to hold officials accountable for abuse -- incidence of abuse is common. Operation Streamline Main article : Operation Streamline Federal courthouse in Tucson, AZ, where Operation Streamline proceedings take place Operation Streamline refers collectively to zero - tolerance policies implemented at the Mexico -- U.S. border that seek to remove undocumented immigrants through an expedited process if they have arrived with missing or fraudulent identification or have previously been convicted for an immigration crime. ICE ERO officers deporting a man wanted for two murders in Mexico History Operation Streamline was first implemented in Del Rio, Texas, in 2005. The program has since expanded to four out of the five federal judicial districts on the U.S. - Mexico border : Yuma, Arizona ; Laredo, Texas ; Tucson, Arizona ; and Rio Grande Valley, Texas. Previously, immigrants apprehended at the border were either given the option to voluntarily return to their home country or they were placed in civil immigration proceedings. After Operation Streamline was implemented, nearly all people apprehended at the border who are suspected of having crossed illegally are subject to criminal prosecution. Defendants who are charged with crossing into the U.S. illegally are tried en masse to determine their guilt. Defense attorneys often are responsible for representing anywhere from six to forty immigrants at once. Around 99 % of defendants in Operation Streamline proceedings plead guilty. The defendants are charged with a misdemeanor if convicted of crossing the border illegally for the first time, and a felony if it is a repeat offense. In December 2009, it was decided in United States v. Roblero - Solis that en masse judicial proceedings like those in Operation Streamline violated Rule 11 in the Federal Rules of Criminal Procedure. Rule 11 states that the court must determine that a guilty plea is voluntarily made by addressing the defendant personally in court. The Roblero - Solis case determined that `` personally '' means that the judge must address the defendant in a person - to - person manner. Though many courts have changed their procedures to adapt to the ruling, there are still forms of en masse trials practiced at the border. Support and criticisms Proponents of Operation Streamline claim that the harsher prosecution has been an important factor in deterring immigrants from crossing the border illegally. Apprehensions have decreased in certain sectors after 2005, which is seen as a sign of success. For example, the Del Rio, Texas, sector saw a decline from 2005 to 2009 of 75 % ( from 68,510 to 17,082 ). Similarly, apprehensions declined in Yuma, Arizona, by 95 % ( from 138,438 to 6,951 ) from 2006 to 2009. Criticisms of Operation Streamline point to the program 's heavy use of federal court and enforcement resources as a negative aspect. In addition, the prosecution of all illegal border crossings takes the focus away from prosecuting more serious crimes. They claim that the program 's cost is too high for the effectiveness of the work it is accomplishing. In response to the claim that Operation Streamline is an effective deterrent, critics of the program claim that the incentives to cross the border in order to work or be with family are much stronger. Environment Further information : Environmental issues along the Mexico -- United States border History The Agreement on Cooperation for the Protection and Improvement of the Environment in the Border Area, known as the La Paz Agreement, was signed into law on August 14, 1983, and became enforceable on February 16, 1984. This agreement to protect the environment is the political foundation between the U.S. and Mexico for 4 subsequent programs. Each program has addressed environmental destruction in the border region resulting from the rise of the maquiladora industries, those who migrated to Northern Mexico to work in the industries, the lack of infrastructure to accommodate the people, Mexico 's lax regulations concerning all these factors, the resulting spillover into the U.S., and the U.S. 's own environmentally destructive tendencies. The programs were : IBEP ( 1992 ), Border XXI ( 1996 ), Border 2012 ( 2003 ) and Border 2020 ( 2012 ). Impacts of border wall on wildlife In 2006, during the presidency of George W. Bush, Congress approved Secure Fence Act which allowed the Department of Homeland Security to erect a border fence along the United State and Mexico border. A total of $2.2 billion was allocated to building this wall in five different areas of the border. Congress also approved a different law called the REAL ID Act which gave the Department of Homeland Security the approval to build the wall without taking into consideration the environmental and legal issues related to the wall. The United States Congress insisted that the act was passed for the sake of national security of the United States. According to a delegation of Arizona park and refuge managers, wildlife biologists, and conservationists who studied the United State and Mexico border concluded that building a wall along the Mexico border will also have negative impacts on the natural environment in the region. They argued that the border wall will negatively affect the wildlife in the Sonoran Desert including plants and animals. Naturally, animals do not tend to stay in one place and instead, they expedite to various places for water, plants, and other means in order to survive. The wall would restrict animals to a specific territory and would reduce their chances of survival. According to Brian Segee, a staff attorney with Wildlife Activists says that except high flying birds, the rest of the animals would not be able to move to other places due to the wall along the border. For instance, participants in this study argued that some of the animal kinds such as javelinas, ocelots, and Sonoran pronghorn would not be able to freely move along the border areas. It would also restrict the movement of jaguars from Sierra Madre Occidental forests to the southwestern parts of the United States. According to Brian Nowicki, a conservation biologist at the Center for Biological Diversity, there are 30 animal species living in the Arizona and Sonora that face danger and their movement to find new habitat and sources of survival would be restricted by the border wall. Travel Passport stamp upon arrival in Tijuana, Baja California land border crossing Western Hemisphere travel Initiative Main article : Western Hemisphere Travel Initiative In late 2006, the United States Department of Homeland Security ( DHS ) announced a rule regarding new identification requirements for U.S. citizens and international travelers entering the United States implemented on January 23, 2007. This final rule and first phase of the WHTI specifies nine forms of identification, one of which is required to enter the United States by air : a valid passport ; a passport card ; a state enhanced driver 's license or state enhanced non-driver ID card ( available in Michigan, New York, Vermont, and Washington ) approved by the Secretary of Homeland Security ; a trusted traveler program card ( NEXUS, FAST, or SENTRI ) ; an enhanced tribal identification card ; a Native American Tribal Photo Identification Card ; Form I - 872 -- American Indian Card ; a valid Merchant Mariner Document when traveling in conjunction with official maritime business ; or a valid U.S. military identification card when traveling on official orders. The San Ysidro border crossing between San Diego and Tijuana The Mexico -- United States border is the world 's busiest border, specifically the crossing at San Diego, California, to Tijuana, Baja California ( 15.6 miles between the cities ), known as the San Ysidro Port of Entry. In the U.S., Interstate 5 crosses directly to Tijuana, and the highway 's southern terminus is this crossing. In 2005, more than 17 million vehicles and 50 million people entered the U.S. through San Ysidro. Among those who enter the United States through San Ysidro are transfronterizos, American citizens who live in Mexico and attend school in the United States. Along the coast of Baja California, there are neighborhoods of Americans living in Tijuana, Rosarito Beach, and Ensenada, whose residents commute to the United States daily to work. Additionally, many Mexicans also enter the United States to commute daily to work. In 1999, 7.6 % of the labor force of Tijuana was employed in San Diego. Barrier Main article : Mexico -- United States barrier The U.S. government had plans in 2006, during the Bush administration, to erect a border fence along the Mexico -- U.S. border. The controversial proposal included creating many individual fences. Almost 600 miles ( 970 km ) of fence was constructed, with each of the individual fences composed of steel and concrete. In between these fences are infrared cameras and sensors, National Guard soldiers, and SWAT teams on alert, giving rise to the term `` virtual fence ''. Construction on the fence began in 2006, with each mile costing the U.S. government about $2.8 million. In 2010, the initiative was terminated due to costs, after having completed 640 miles ( 1,030 km ) of either barrier fence or vehicle barriers, that were either new or had been rebuilt over older, inferior fencing. The Boeing - built SBI - net systems of using radar, watchtowers, and sensors ( without a fence or physical barrier ) were scrapped for being over budget, full of glitches, and far behind schedule. The U.S. -- Mexico border fence near El Paso, Texas Portion of border near Jacumba, California, in 2003 Portion of border near Jacumba, California, in 2009 with enhanced security Veterinary inspections When animals are imported from one country to another, there is the possibility that diseases and parasites can move with them. Thus, most countries impose animal health regulations on the import of animals. Most animals imported to the United States must be accompanied by import permits obtained in advance from the U.S. Department of Agriculture 's Animal and Plant Health Inspection Service ( APHIS ) and / or health certification papers from the country of origin. Veterinary inspections are often required, and are available only at designated ports ; advance contact with port veterinarians is recommended. Animals crossing the United States -- Mexico border may have a country of origin other than the country where they present for inspection. Such animals include those from the U.S. that cross to Mexico and return, and animals from other countries that travel overland through Mexico or the U.S. before crossing the border. Crossing from Mexico to the United States APHIS imposes precautions to keep out several equine diseases, including glanders, dourine, equine infectious anemia ( EIA ), equine piroplasmosis ( EP ), Venezuelan equine encephalitis ( VEE ), and contagious equine metritis ( CEM ). APHIS also checks horses to prevent the introduction of ticks and other parasites. In the Lower Rio Grande Valley, U.S. Department of Agriculture inspectors look for horses and livestock that stray across the border carrying ticks. These animals are often called wetstock, and the inspectors are referred to as tickriders. Per APHIS, horses originating from Canada can enter the United States with a Canadian government veterinary health certificate and a negative test for EIA. Horses from Mexico must have a health certificate ; pass negative tests for EIA, dourine, glanders, and EP at a USDA import center ; and undergo precautionary treatments for external parasites at the port of entry. Horses from other Western Hemisphere countries must have the same tests as those from Mexico and, except for horses from Argentina, must be held in quarantine for at least seven days as a check for VEE. APHIS imposes similar testing and certification requirements on horses from other parts of the world but without the quarantine for VEE. These horses are held in quarantine -- usually three days -- or until tests are completed. Because the disease equine piroplasmosis ( equine babesiosis ) is endemic in Mexico but not established in the United States, transportation of horses from Mexico to the United States requires evaluation of horses for the presence of this disease. Transportation of horses from Mexico to the United States normally requires at least three days in quarantine, which is incompatible with most recreational equestrian travel across the border. A leading exception to this rule is the special waiver obtained by riders participating in the Cabalgata Binacional Villista ( see cavalcade ). Crossing from the United States to Mexico Import from the United States to Mexico requires evidence within the prior 45 days of freedom from equine infectious anemia, among other requirements. In August 2015, Mexico began enforcing a rule that all foreign citizens that plan to stay in the country for more than seven days or are travelling on business will have to pay a 330 peso ( 21 dollar ) fee and show their passport. See also Mexico portal United States portal International relations portal Mexico -- United States barrier 2017 Mexico -- United States diplomatic crisis Border Protection, Anti-terrorism, and Illegal Immigration Control Act of 2005 List of municipalities ( municipios ) and counties on the Mexico -- United States border Migrant deaths along the Mexico -- United States border Secure Fence Act of 2006 Sexual assault of migrants from Latin America to the United States Treaty of Limits ( Mexico -- United States ) United States Border Patrol interior checkpoints Canada -- United States border References ^ Jump up to : Golson, Barry ; Thia Golson ( 2008 ). Retirement Without Borders : How to Retire Abroad -- in Mexico, France, Italy, Spain, Costa Rica, Panama, and Other Sunny, Foreign Places. New York, New York : Simon & Schuster. p. 75. ISBN 978 - 0 - 7432 - 9701 - 1. Retrieved March 9, 2011. ^ Jump up to : `` US, Mexico open first new border crossing in 10 years ''. AFP. Washington. January 12, 2010. Archived from the original on February 28, 2014. Retrieved December 3, 2012. The US - Mexico border is the busiest in the world, with approximately 350 million crossings per year. ^ Jump up to : Edwin Mora ( May 19, 2010 ). `` Senate Democratic Whip Compares Sealing the Mexican Border to Trying to Keep Drugs Off of I - 95 ''. Cybercast News Service. Retrieved March 9, 2011. ^ Jump up to : Glenday, Craig ( 2009 ). Guinness World Records 2009. Random House Digital, Inc. p. 457. ISBN 978 - 0 - 553 - 59256 - 6. Retrieved March 9, 2011. Jump up ^ http://www.ibwc.gov/About_Us/about_us.html Jump up ^ Loustaunau, M., & Bane, M. ( 1999 ). Life, death, and in - between on the u.S. - Mexico border : Asi es la vida. Westport, Conn. : Bergin & Garvey. https://ebookcentral.proquest.com/lib/beloit-ebooks/reader.action?docID=496818 Jump up ^ `` Treaty to Resolve Pending Boundary Differences and Maintain the Rio Grande and Colorado River as the International Boundary between the United States of America and México '' ( PDF ). November 23, 1970. Retrieved December 7, 2014. ^ Jump up to : McCarthy, Robert J. ( Spring 2011 ). `` Executive Authority, Adaptive Treaty Interpretation, and the International Boundary and Water Commission, U.S. - Mexico ''. Water Law Review. University of Denver : 3 -- 5. SSRN 1839903. Jump up ^ https://www.ibwc.gov/About_Us/about_us.html Jump up ^ `` United States Section Directive '' ( PDF ). Archived from the original ( PDF ) on October 15, 2011. Retrieved November 11, 2011. Jump up ^ https://www.epa.gov/sites/production/files/2015-09/documents/lapazagreement.pdf Jump up ^ https://www.cdc.gov/usmexicohealth/about-border-region.html Jump up ^ `` The United States - Mexico Border Region at a Glance '' ( PDF ). United States - Mexico Border Health Commission. New Mexico State University. Archived from the original ( PDF ) on September 15, 2012. Retrieved December 3, 2012. In 2001, over 300 million two - way border crossings took place at the 43 POEs. ^ Jump up to : Hodge, Roger D. ( 2012 ). `` Borderworld : How the U.S. Is Reengineering Homeland Security ''. Popular Science. 280 ( 1 ) : 56 -- 81. Jump up ^ Martínez, Oscar J. ( 1988 ). Troublesome Border. Tucson : University of Arizona Press. ISBN 978 - 0 - 8165 - 1104 - 4. Jump up ^ `` Treaty of Guadalupe Hidalgo ''. www.ourdocuments.gov. 1848. Retrieved December 6, 2014. Jump up ^ Byrd, Bobby ; Mississippi, Susannah, eds. ( 1996 ). The Late Great Mexican Border : Reports from a Disappearing Line. El Paso : Cinco Puntos Press. ISBN 0 - 938317 - 24 - 5. ^ Jump up to : `` The U.S. - Mexico border : under the economic lens and in the historical frame ''. pulsamerica.co.uk. ^ Jump up to : `` Borders and Identity ''. smithsonianeducation.org. Jump up ^ Hart, John M. ( 2000 ). `` The Mexican Revolution, 1910 -- 1920 ''. Oxford History of Mexico. New York : Oxford University Press. pp. 433 -- 66. ISBN 0 - 19 - 511228 - 8. ^ Jump up to : Lorey, David E. ( 1999 ). The U.S. - Mexican Border in the Twentieth Century. Wilmington : Scholarly Resources, Inc. ISBN 0 - 8420 - 2756 - 4. Jump up ^ Options for Estimating Illegal Entries at the U.S. - Mexico Border The National Academies Press. Washington D.C. : The National Academies Press. 2013. doi : 10.17226 / 13498. ISBN 978 - 0 - 309 - 26426 - 6. Jump up ^ Martínez, Ruben ( 2004 ). `` Fortress America ''. Index on Censorship. 33 ( 3 ) : 48 -- 52. Jump up ^ `` Border Patrol Overview ''. cbp.gov. ^ Jump up to : Vulliamy, Ed ( 2010 ). Amexica : War Along the Borderline. Farrar, Straus and Giroux. ISBN 978 - 0 - 374 - 10441 - 2. Jump up ^ U.S. Department of Homeland Security ( June 23, 2010 ). `` Fact Sheet : Southwest Border Next Steps ''. Retrieved August 6, 2010. Jump up ^ Jeffrey, Terence P. ( September 24, 2009 ). `` Administration Will Cut Border Patrol Deployed on U.S - Mexico Border ''. Cybercast News Service. Archived from the original on December 9, 2009. Retrieved September 25, 2009. Jump up ^ Terence P. Jeffrey ( March 31, 2011 ). `` Federal Auditor : Border Patrol Can Stop Illegal Entries Along Only 129 Miles of 1,954 - Mile Mexican Border ''. Cybercast News Service. Retrieved March 31, 2011. Jump up ^ `` BORDER PATROL : Available Data on Interior Checkpoints Suggest Differences in Sector Performance '' ( PDF ). United States General Accounting Office. July 2005. Jump up ^ `` BORDER PATROL : Checkpoints Contribute to Border Patrol 's Mission, but More Consistent Data Collection and Performance Measurement Could Improve Effectiveness '' ( PDF ). United States General Accounting Office. August 2009. Jump up ^ Aduana Mexico ( 2007 ). `` Aduanas 25 de las Reglas de Caracter General en Materia de Comercio Exterior para 2007 '' ( in Spanish ). Archived from the original on February 24, 2012. ^ Jump up to : `` Illegal Immigration -- Border - Crossing Deaths Have Doubled Since 1995 ; Border Patrol 's Efforts to Prevent Deaths Have Not Been Fully Evaluated '' ( PDF ). Government Accountability Office. August 2006. p. 42. ^ Jump up to : Dinan, Stephen ( January 9, 2013 ). `` Interceptions of immigrants stubbornly low ''. Washington Times. Retrieved January 12, 2013. Jump up ^ Options for estimating illegal entries at the U.S. - Mexico border. https://ebookcentral.proquest.com/lib/beloit-ebooks/reader.action?docID=3379100 Jump up ^ `` Report : Border Patrol confirms 29 incursions by Mexican officials into U.S. in 2007 ''. San Diego Union Tribune. Retrieved January 17, 2008. Jump up ^ `` MSNBC report on Border incursion Oct 18 2007 ''. MSNBC. Retrieved January 17, 2008. Jump up ^ `` Mexican incursions inflame border situation ''. MSNBC. Retrieved January 17, 2008. Jump up ^ `` DHS to Hunter : More than 300 border incursions by Mexican military and law enforcement authorities since January 2004 ''. Congressman Duncan Hunter. United States House of Representatives. June 17, 2014. Retrieved June 17, 2014. Jump up ^ `` Border patrol agent held at gunpoint ''. Washington Times. August 8, 2008. Jump up ^ Potter, Mark. `` Debate rages over Mexico ' spillover violence ' in U.S. '' NBC News. Retrieved September 24, 2012. Jump up ^ `` Further Buildup on US - Mexico Border Unnecessary : Report ''. InSight Crime. April 20, 2012. Retrieved December 7, 2014. Jump up ^ CNN, Stephen Collinson and Jeremy Diamond. `` Mexican president disputes Trump over border wall payment discussion ''. CNN. Retrieved October 7, 2016. Jump up ^ `` How realistic is Donald Trump 's Mexico wall ? ''. BBC News. September 1, 2016. Retrieved October 7, 2016. Jump up ^ BBC News ( January 26, 2017 ). `` Trump orders wall to be built on Mexico border ''. BBC News. Retrieved January 26, 2017. Jump up ^ BBC News ( January 26, 2017 ). `` Mexico : We will not pay for Trump border wall ''. BBC News. Retrieved January 26, 2017. Jump up ^ Reuters ( January 26, 2017 ). `` Trump seeks 20 percent tax on Mexico goods to pay for wall, crisis deepens ''. Reuters. Retrieved January 26, 2017. ^ Jump up to : https://www.washingtonpost.com Republicans skeptical about paying for wall as Trump releases budget. Jump up ^ latimes.com : California again steps up to Trump, this time to stop the border wall Jump up ^ State of California Department of Justice, September 20, 2017 : Attorney General Becerra : Constitution, Rule of Law Barriers to Trump Border Wall ( Press Release ) Jump up ^ U.S. Moves to Build Prototypes for Mexican Border Wall. U.S. Moves to Build Prototypes for Mexican Border Wall. https://www.nytimes.com/2017/08/31/us/mexico-wall-prototypes-trump.html Jump up ^ THE WALL The real costs of a barrier between the United States and Mexico. https://www.brookings.edu/essay/the-wall-the-real-costs-of-a-barrier-between-the-united-states-and-mexico/ Jump up ^ Golash - Boza, Tanya Maria ( 2015 ). Deported : Policing Immigrants, Disposable Labor and Global Capitalism. New York City, New York : New York University Press. pp. 61 -- 61 -- 62. ISBN 978 - 1 - 4798 - 5944 - 3. ^ Jump up to : `` Population and Development Review ''. Population Council. 27 : 661 -- 676. December 2001 -- via JSTOR. ^ Jump up to : Seghetti, Lisa ( December 31, 2014 ). `` Border Security : Immigration Enforcement Between Ports of Entry '' ( PDF ). Congressional Research Service. ^ Jump up to : `` The Constitution in the 100 - Mile Border Zone ''. American Civil Liberties Union. Jump up ^ Rickerd, C. `` Customs and Border Protection 's ( CBP 's ) 100 - Mile Rule '' ( PDF ). American Civil Liberties Union. ^ Jump up to : Lydgate, L. ( 2010 ). `` Assembly - Line Justice : A Review of Operation Streamline ''. California Law Review. 98 ( 2 ) : 481 -- 544. JSTOR 20743978. ^ Jump up to : Nazarian, E. ( 2011 ). `` Crossing Over : Assessing Operation Streamline and the Rights of Immigrant Criminal Defendants at the Border ''. Loyola of Los Angeles Law Review. 44 : 1399 -- 430. Archived from the original on 2011. ^ Jump up to : Kerwin, D. ; McCabe, K. `` Arrested on Entry : Operation Streamline and the Prosecution of Immigration Crimes ''. Migration Policy Institute. Jump up ^ `` Agreement on Cooperation for the Protection and Improvement of the Environment in the Border Area '' ( PDF ). US Environmental Protection Agency. 1983. Retrieved December 2, 2014. Jump up ^ Smith, Colin. `` 1 U.S. -- Mexico Cooperation for the Health of the Environment in the Border Region : A Policy History Analysis ''. Archived from the original on November 13, 2013. ^ Jump up to : The Environmental Impacts of a Border Fence. https://www.jstor.org/stable/pdf/10.1641/b570116.pdf Jump up ^ `` WHTI : Enhanced Drivers License ''. Jump up ^ DHS Announces Final Western Hemisphere Air Travel, Association of Cotpotrate Travel Executives, December 5, 2006, archived from the original on December 16, 2007, retrieved December 2, 2007 Jump up ^ Western Hemisphere Travel Initiative : The Basics, U.S. Department of Homeland Security, archived from the original on December 26, 2007, retrieved December 2, 2007 Jump up ^ Western Hemisphere Travel Initiative, U.S. Department of State, Bureau of Consular Affairs, January 13, 2008, archived from the original on January 25, 2007, retrieved January 12, 2007 Jump up ^ `` Traveling to USA ? ''. archive.org. Archived from the original on September 11, 2004. Jump up ^ Sandra Dibble ( July 11, 2010 ). `` Number of border crossings stabilizes ''. San Diego Union Tribune. Retrieved January 5, 2013. Jump up ^ OECD ( September 28, 2010 ). Regional Development Policies in OECD Countries. OECD Publishing. p. 331. ISBN 978 - 92 - 64 - 08725 - 5. Jump up ^ Berndes, Barry ( 2009 ). The SAN DIEGAN -- 41st Edition. The SAN DIEGAN. p. 227. ISBN 978 - 1 - 890226 - 13 - 8. Jump up ^ Gaynor, Tim ( 2009 ). Midnight on the Line : The Secret Life of the U.S. - Mexico Border. Macmillan. p. 81. ISBN 978 - 1 - 4299 - 9462 - 0. Jump up ^ Border Security : Despite Progress, Weaknesses in Traveler Inspections Exist at Our Nation 's Port of Entry ( PDF ). United States Government Accountability Office. November 2007. p. 10. GAO - 08 - 219. Retrieved September 8, 2014. and the busiest land crossing in the United States at San Ysidro, California, which processes over 17 million vehicles a year ( see fig. 1 ) ; Jump up ^ Brown, Patricia Leigh ( January 16, 2012 ). `` Young U.S. Citizens in Mexico Brave Risks for American Schools ''. New York Times. Retrieved September 8, 2014. Jump up ^ Yogerst, Joe ; Mellin, Maribeth ( 2002 ). Traveler 's Companion California. Globe Pequot. p. 341. ISBN 978 - 0 - 7627 - 2203 - 7. Retrieved September 8, 2014. Jump up ^ Levine, Robert N. ( 2008 ). A Geography Of Time : On Tempo, Culture, And The Pace Of Life. Basic Books. p. 190. ISBN 978 - 0 - 7867 - 2253 - 2. Retrieved September 8, 2014. Jump up ^ Mendoza, Cristobal ; Loucky, James ( 2008 ). `` Recent Trends in Mexico - U.S. Border Demographics ''. In Alper, Donald K. ; Day, John Chadwick ; Loucky, James. Transboundary Policy Challenges in the Pacific Border Regions of North America. University of Calgary Press. p. 55. ISBN 978 - 1 - 55238 - 223 - 3. Jump up ^ Hsu, Spencer S. ( March 16, 2010 ). `` Work to cease on ' virtual fence ' along U.S. - Mexico border ''. The Washington Post. Jump up ^ `` Ports Designated for the Importation of Animals ''. Animal and Plant Health Inspection Service ( APHIS ). Archived from the original on February 2, 2007. Retrieved October 5, 2011. Jump up ^ `` Port Veterinarian List ''. Animal and Plant Health Inspection Service ( APHIS ). Archived from the original on December 9, 2006. Retrieved October 5, 2011. ^ Jump up to : `` Equine Importation ''. Animal and Plant Health Inspection Service ( APHIS ). Archived from the original on October 17, 2010. Retrieved October 5, 2011. Jump up ^ Miller, Tom ( 2000 ). On the Border : Portraits of America 's Southwestern Frontier. iUniverse. pp. 72 -- 73. ISBN 978 - 0 - 595 - 14334 - 4. Jump up ^ `` Veterinary Science ''. Jump up ^ `` Import health requirements of Mexico for horses ( non slaughter ) exported from the United States '' ( PDF ). Animal and Plant Health Inspection Service ( APHIS ). December 2005. Archived from the original ( PDF ) on April 19, 2009. Retrieved October 5, 2011. Jump up ^ San Diego Union Tribune : `` New pedestrian crossing unveiled in Tijuana '' by Sandra Dibble August 19, 2015 Jump up ^ Christian Science Monitor : `` Why it 's Mexico 's turn to tighten the US border -- A checkpoint at the nation 's busiest border crossing will now require Americans to show their passports before entering Mexico '' By Michelle Toh August 20, 2015 Jump up ^ National Public Radio : `` New Rules Go Into Effect At Busy U.S. - Mexico Border Crossing '' by Laura Wagner August 20, 2015 Parts of this article have been adapted from The International Boundary and Water Commission, Its Mission, Organization and Procedures for Solution of Boundary and Water Problems. Arbelaez, Harvey, and Claudio Milman. `` The New Business Environment of Latin America and the Caribbean ''. International Journal of Public Administration ( 2007 ) : 553 Kelly, Patricia, and Douglas Massey. `` Borders for Whom ? The Role of NAFTA in Mexico - U.S. Migration ''. The ANNALS of the American Academy of Political Science 610 ( 2007 ) : 98 -- 118. Miller, Tom. On the Border : Portraits of America 's Southwestern Frontier, 1981. Thompson, Olivia N. ( 2009 ). `` Binational Water Management : Perspectives of Local Texas Officials in the U.S. - Mexico Border Region ''. Applied Research Projects. Texas State University. Paper 313. Andrew Becker and Agustin Armendariz. `` California Border Crossing : San Ysidro Port Of Entry Is The Busiest Land Border In The World '' ( 1 ) HuffPost social reading, article on California watch. ( 2012 ) Prampolini, Gaetano, and Annamaria Pinazzi ( eds ). `` The Shade of the Saguaro / La sombra del saguaro '' Part IV ' About the Border '. Firenze University Press http://www.fupress.com/ ( 2013 ) : 461 - 517. Further reading Border Town -- Dallas Observer External links Wikimedia Commons has media related to Mexico -- United States border. U.S. - Mexico Business Council Border Stories : a mosaic documentary on the U.S. - Mexico Border Status of Mexican Trucks in the United States : Frequently Asked Questions Congressional Research Service A Continent Divided : The U.S. - Mexico War, Center for Greater Southwestern Studies, the University of Texas at Arlington Josh Begley, Best of Luck with the Wall -- a short film constructed from satellite imagery that traces the length of the border David Taylor, The Journey to Border Monument Number 140 -- photographs and description of the obelisks that mark the border Peter Bo Rappmund, Tectonics -- photographs and feature - length film that follows the infrastructure of the border from the Gulf of Mexico to the Pacific Ocean Immigration to the United States and related topics Relevant colonial era, United States and international laws Colonial era Nationality law in the American Colonies Plantation Act 1740 18th century Naturalization Act 1790 / 1795 / 1798 19th century Naturalization Law 1802 Civil Rights Act of 1866 14th Amendment ( 1868 ) Naturalization Act 1870 Page Act ( 1875 ) Immigration Act of 1882 Chinese Exclusion ( 1882 ) Scott Act ( 1888 ) Immigration Act of 1891 Geary Act ( 1892 ) 1900 -- 1949 Naturalization Act 1906 Gentlemen 's Agreement ( 1907 ) Immigration Act of 1907 Immigration Act 1917 ( Asian Barred Zone ) Emergency Quota Act ( 1921 ) Cable Act ( 1922 ) Immigration Act 1924 Tydings -- McDuffie Act ( 1934 ) Filipino Repatriation Act ( 1935 ) Nationality Act of 1940 Bracero Program ( 1942 -- 1964 ) Magnuson Act ( 1943 ) War Brides Act ( 1945 ) Luce -- Celler Act ( 1946 ) 1950 -- 1999 UN Refugee Convention ( 1951 ) Immigration and Nationality Act 1952 / 1965 Refugee Act ( 1980 ) Immigration Reform and Control Act ( 1986 ) American Homecoming Act ( 1989 ) Immigration Act 1990 Illegal Immigration Reform and Immigrant Responsibility Act ( IIRIRA ) ( 1996 ) Nicaraguan Adjustment and Central American Relief Act ( NACARA ) ( 1997 ) American Competitiveness and Workforce Improvement Act ( ACWIA ) ( 1998 ) 21st century American Competitiveness in the 21st Century Act ( AC21 ) ( 2000 ) Legal Immigration Family Equity Act ( LIFE Act ) ( 2000 ) H - 1B Visa Reform Act ( 2004 ) REAL ID Act ( 2005 ) Secure Fence Act ( 2006 ) DACA ( 2012 ) Executive Order 13769 ( 2017 ) Executive Order 13780 ( 2017 ) Visas and policies Visa policy Permanent residence Visa Waiver Program Temporary protected status Asylum Green Card Lottery US - VISIT Security Advisory Opinion E-Verify Section 287 ( g ) National Origins Formula Government organizations Department of Homeland Security Immigration and Customs Enforcement U.S. Border Patrol U.S. Customs and Border Protection Immigration and Naturalization Service ( INS ) Board of Immigration Appeals Supreme Court cases United States v. Wong Kim Ark ( 1898 ) United States v. Bhagat Singh Thind ( 1923 ) United States v. Brignoni - Ponce ( 1975 ) Chamber of Commerce v. Whiting ( 2011 ) Related issues and events Economic impact Eugenics in the United States Guest worker program Human trafficking Human smuggling Coyotaje Immigration reform Immigration reduction Mexico -- United States barrier Labor shortage March for America Illegal immigrant population Reverse immigration 2006 protests Unaccompanied minors from Central America List of people deported from the United States Geography Mexico -- United States border Canada -- United States border United States Border Patrol interior checkpoints Proposed legislation DREAM Act ( 2001 -- 2010 ) H.R. 4437 ( 2005 ) McCain -- Kennedy ( 2005 ) SKIL ( 2006 ) Comprehensive Immigration Reform Act 2006 STRIVE Act ( 2007 ) Comprehensive Immigration Reform Act 2007 Uniting American Families Act ( 2000 -- 2013 ) Border Security, Economic Opportunity, and Immigration Modernization Act of 2013 SAFE Act ( 2015 ) RAISE Act ( 2017 ) Immigration stations and points of entry Angel Island Castle Garden East Boston Ellis Island Sullivan 's Island Washington Avenue Operations `` Wetback '' ( 1954 ) `` Peter Pan '' ( 1960 -- 1962 ) `` Babylift '' ( 1975 ) `` Gatekeeper '' ( 1994 ) `` Endgame '' ( 2003 -- 2012 ) `` Front Line '' ( 2004 -- 2005 ) `` Streamline '' ( 2005 -- present ) `` Return to Sender '' ( 2006 -- 2007 ) `` Jump Start '' ( 2006 -- 2008 ) State legislation California DREAM Act ( 2006 -- 2010 ) Arizona SB 1070 ( 2010 ) Alabama HB 56 ( 2011 ) Non-governmental organizations Arizona Border Recon Coalition for Humane Immigrant Rights of Los Angeles Coalition for Comprehensive Immigration Reform National Immigration Forum Center for Community Change We Are America Alliance CASA of Maryland Mexica Movement Mexicans Without Borders Federation for American Immigration Reform Minuteman Project Minuteman Civil Defense Corps California Coalition for Immigration Reform Save Our State Center for Immigration Studies National Korean American Service & Education Consortium ( NAKASEC ) NumbersUSA Negative Population Growth Migration Policy Institute Utah Compact Center for Migration Studies of New York Borders of Mexico United States Belize Guatemala Retrieved from `` https://en.wikipedia.org/w/index.php?title=Mexico -- United_States_border&oldid = 832925772 '' Categories : Geography of Arizona Geography of California Geography of New Mexico Geography of Texas Mexico -- United States border Southwestern United States Borders of the United States Borders of Mexico Hidden categories : CS1 Spanish - language sources ( es ) Use mdy dates from November 2017 Articles needing additional references from December 2014 All articles needing additional references Articles which use infobox templates with no data rows All articles with vague or ambiguous time Vague or ambiguous time from April 2017 NPOV disputes from December 2017 All NPOV disputes Articles needing additional references from March 2015 Talk Contents About Wikipedia Bân - lâm - gú Български Català Deutsch Español فارسی Français 한국어 Italiano Bahasa Melayu Nederlands 日本 語 Norsk Polski Português Русский Shqip Simple English Svenska Tiếng Việt 中文 12 more Edit links This page was last edited on 28 March 2018, at 18 : 31. 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Question: what four states in the us form the northern border of mexico
Answer: California