Nature created a convenient international boundary with the Rio Grande River, which slashes the southwestern desert to divide Texas from Mexico.
While the 1,200-mile border creates a distinctive break in the open spaces of this region, the intangibles of the Texan and Mexican cultures and economies respect no borders.
For this reason, the recent dip of the Mexican economy has inextricably taken the Texas border area along for the ride. Mexico has long benefited from bursts of Texas prosperity, including the one of the past decade.
Perhaps no boundary in the world has such a volatile juxtaposition of a poor nation up against a rich nation.
Texas and Mexico, however, share more than a common frontier. The Mexican flavor, which is not just hot sauce, has become ingrained in Texas lifestyles - from the Spanish language, to architectural styles, to the large number of Hispanics (21 percent) in the population, and to the Mexican-Americans growing - although not fully utilized - economic and political power.
Mexico's recent international loan crisis, which brought the nationalization of Mexican banks and the second collapse of the peso in six months, cast a shadow of economic uncertainty that creeps into US affairs at the national level , but is likely to be felt most heavily in the US-Mexioco border region - two-thirds of it in Texas.
''Whatever pain and suffering there is in Mexico (because of the economy) there's pain and suffering just across the border too,'' says Dr. Richard Rubottom, a Southern Methodist University professor emeritus, former diplomat, and now advisor to Gov. William Clements on relations with Mexico. ''But out of the crisis there can and should flow opportunity for a more constructive, coordinated, and understanding relationship.
''Whether it be Bank of America (the largest foreign bank operating in Mexico) or the boutique in Brownsville that's not selling a nickel,'' the point is being driven home to Americans that Mexican interests are also US interests, Dr. Rubottom says.
While the federal government sets diplomatic policy, the ultimate responsibility for the day to day business and cultural relations with Mexico rests with regional authorities. For example, federal law may set rules for immigration, but the issue of providing for the education, welfare, and monitoring of those Mexicans flowing into the United States - both legally and illegally at the estimated rate of about 1 million annually - invariably is in the hands of state and local agencies.
Of about $2 billion spent by Mexican tourists in the US, three-quarters is spent in border states. Further, much of the industrial growth in Texas has resulted from the cheap - some critics claim ''slave'' - labor provided by Mexicans.
One example of the benefits of cheap labor is the twin-plants projects: US-owned plants in Mexico assemble products or parts and re-export them, duty-free, to the US.
While statistics show that Mexico does most of its business with the US, the data lopsidedly shows that the US perhaps benefits more from the relationship. For example, Mexico's bright oil-production prospects are shadowed by a dependence on the giant to the north: Mexico exports 60 percent of its crude oil to the US, but that accounts for only 7 percent of the US imports.
Texas, the only state with a Mexico City office, has chosen to take on an almost diplomatic relationship with Mexico in its efforts to meld its phenomenal growth with the potential of the border region. And the state has chosen to work directly with Mexico on certain key issues that stand to affect the quality of life and business on both sides of the border. Some of the issues identified include:
* Assuring that regional concerns are considered in the design of immigration and illegal-drug-control programs.
* Developing bilingualism.
* Developing clean-air and water standards that are agreeable to both countries to control oil drilling and industrial wastes that threaten the environment