When the dry grass they use to make brooms at a Palomas, Mexico, factory caught fire a few weeks ago, tiny Columbus, N.M., sent its fire engine careening across the international border to battle the blaze.
It's a regular event, says Columbus Mayor Carlos Ogden, who adds that without the border crossing station there would be little distinction between his town (pop. 500) and Palomas (pop. 4,500).
Eric Rice, a Calexico, Calif., school district official, sent his son to private schools across the border in Mexicali, the capital of Baja California, until the boy graduated from sixth grade. Mr. Rice, like several dozen other Imperial Valley Anglo parents who cart their children daily through border inspection stations, wanted his son to be fully versed in the Mexican culture and Spanish language that permeate the border region they live in.
This is just a slice of the daily cultural interchange that takes place between the sets of twin communities that dot the 2,000-mile Mexican-American border - a frontier so porous, some speculate, that it is a culture and nation unto itself.
The stereotypical picture of the border is a collision of Anglo and Latin, rich and poor. But those differences are complemented by the ''border culture,'' which is a an amalgam of international differences.
''Our southern frontier is not simply American on one side and Mexican on the other,'' author Tom Miller observes in his book ''On the Border,'' a group of lively stories gathered during a four-month journey weaving back and forth across the border from Brownsville-Matamoros to Tijuana-San Diego. ''It is a third country with its own identity. . . . Its food, its language, its music are its own. Even its economic development is unique. It is a colony unto itself, long and narrow, ruled by two faraway powers.''
Independent of Mr. Miller, Manuel Carlos, an anthropologist at the University of California, Santa Barbara, also concludes that ''in a figurative sense, the borderland is a third nation.''
''Americans are becoming Mexicanized, and Mexicans are becoming Americanized, along a border which is totally permeable - economically, socially, and culturally,'' he says. The Sunbelt magnet has brought rapid growth in the area, drawing migrants from villages in the interior of Mexico as well as from the Northeastern United States. (Tijuana, for example, a dusty village of 20,000 50 years ago, has passed the 1 million mark.) Government agencies, schools, communications media, and businesses on both sides of the border have had to cooperate as they learned that human problems do not respect man-made borders.
On the other hand, some, like Larry Herzog, a geographer in the urban studies department at California State University at San Diego, are convinced the area is ''very polarized,'' with a tilt toward American power. This tilt is becoming more pronounced as the Sunbelt continues to attract settlers from the US Northeast and the interior of Mexico.
Granted, the margins on either side of the border are full of obvious differences: the orderly grids of US cities and the often chaotic traffic of Mexican towns; the crisp little stucco American suburbs and the dilapidated, corrugated-tin shacks of the poorest Mexicans; the Americans who live within miles of - but never cross - the border, and the thousands of Mexicans who flow across the border daily in search of prosperity.
But here, within 20 miles of the border on each side, is a culture more blended than that of many of America's so-called ''melting pots'' - Boston still has its predominantly Italian North End, New York has its Chinatown, Chicago its little Warsaw. Even Los Angeles has a largely Chicano East Side.
But here there are inextricable ties - border economies depend on the interchange of the some 600 maquiladoras (twin-plant system), tourism, retail sales. Locals can't help picking up a little English or a little Spanish. Mexicans may cross the border to find jobs or purchase American goods as a status symbol, just as Americans cross the border as tourists or to take advantage of bargains such as cheap gasoline or medical or dental services.
Some observers also see subtler cultural nuances that have taken root along the border, nuances that they contend are no less characteristic of border culture than the often-quoted trade and population figures: language, food, attitudes, and customs. The border language incorporates English into Spanish - border Mexicans are apt to say ''troka'' or ''peekup'' for truck, instead of ''camiones.'' Mexican proprietors along the border often post prices in dollars instead of pesos. The ''quincinera'' custom is still embraced by third- and fourth-generation Mexican-Americans, in which girls are given ''coming out'' parties at the age of 15.
The mix of food, media (English and Spanish television, radio, and outdoor advertising), language, and attitudes in this region convinces Mario Carillo that there is a border culture, even though there are those who resent the idea or don't believe it.
Mr. Carillo, director of Tijuana's Center for Border Studies, explains: ''Somehow, culture at the border is not less American or less Mexican, but more of both. It can be a process of enrichment. Culture is not limited - in our being we don't have a box that says 'culture' and just so much space to fill. It's an open space with the capacity to absorb more.''
Others do not subscribe to the border-culture concept. But Carillo suggests that if more people on both sides of the border accepted the idea, the region might be able to address its problems more effectively. Local issues become international only because they happen to cross the border; if more people on both sides of the border recognized it as a region with a shared destiny, common problems might be more easily solved at a local level. (Issues he refers to include problems in areas like pollution, water resources, sewage, education, and immigration.)
There are, of course, those who live along the border and never touch base with the growing biculturalism. Some try to preserve their own heritage, and others simply seem unaware they live within a stone's throw of a foreign country. Many Americans, lifelong border residents, can count on one hand the number of times they've crossed the border. Americans often cite such stereotypes as bad water, unsanitary food, and lawless conditions on the Mexican side.
Border-dwelling Mexicans who haven't encountered life on the American side, however, are usually those who are simply too poor to afford the journey.
Wealthy Tijuana residents, too, who in the worst periods of the peso devaluation continued to buy American goods in San Diego to maintain ''status,'' try to preserve their culture by maintaining ''charro'' clubs - an old-fashioned riding club in which members don the large sombreros and silver-buttoned and embroidered riding outfits, observes Stan Wulff, editor of Fiesta magazine.
Despite those who cling to their respective sides of the border, a separate border culture thrives between them. And there are those who are not reluctant to embrace it. Many in the US are familiar with the Mexican influence on the US side of the border; what is perhaps not so obvious is American culture's impact on the Mexican side.
''There is a small but identifiable border culture (on the Mexican side),'' says Ricardo Chavira, a reporter who covers the border for the San Diego Union. ''It's not only that they speak English, it transcends that. They are thoroughly knowledgeable about the US. . . . They're Charger fans . . . if they lived a few miles north they would be indistinguishable.'' (He is careful to point out that there are many more Mexicans, though, who are poverty stricken and hardly a part of this more affluent border culture.)
While Mexicans more freqently make this bicultural leap, increasing numbers of Americans, too, are recognizing their ties to the south.
More and more Americans live on the Mexican side because the life style is cheaper. Teodoro Arbeso Villarin, an American of Philippine descent who speaks no Spanish, has lived in a beach house in Tijuana for several months now. He pays slightly more than $100 a month for a three-bedroom house that would likely rent for $700 on the US side. He says his life style is so cheap he doesn't mind the often long waits at immigration to go to work in San Diego every day.
In Columbus, N.M., fully one-half of the American public-school children live across the border in Palomas. The cities are inextricably tied in this way, says Mayor Ogden, because there is no hospital in Palomas and Mexican parents have their babies in the Demming hospital 50 miles north. In turn, though, Columbus residents who have no doctor use Palomas's government-paid physicians.
There is a long-held argument in this New Mexico outpost, too, says Ogden, that any Palomas resident should be allowed to attend Columbus schools - currently, they are not. New Mexico schools are funded out of state sales taxes, not property taxes. And fully 70 percent of Columbus's business, he adds, comes from Mexico.
Those who know Eric Rice claim he is a perfect example of a bicultural border resident. Mr. Rice, who grew up in Calexico and was educated in Mexicali schools , says the quality of his life has been enhanced by being able to operate on both sides of the border. That's why he sent his children to Mexicali schools.
''Calexico is over 95 percent Mexican-American, and it's a phenomenon all over the Southwest. You can get up on your high horse and say, 'Let them all learn English,' but you may practice law, teach school, run a store, and the fact of the matter is you'll need it (Spanish),'' Mr. Rice explains. ''Unless you know the feelings, attitudes, inflections, unless you're comfortable with a culture, you may not be able to grasp an issue.'' He adds that he knows good lawyers who routinely present mediocre cases because they can't understand their clients. Rice felt that, for his children to prosper and ''do better than survive,'' they needed to go to the Spanish-speaking Mexicali schools.
Further, he adds, the quality of education in these Roman Catholic church-run schools is very good. He says that in math, the students graduate two years ahead of students in American schools.
Meanwhile, Rice, who runs the personnel department of the Calexico school district, says many Mexicans send their children to both private and public schools on the US side. They pay $1,700 to $1,800 a year tuition at the public schools.
Rice, who also administers translation programs for government agencies, says the Americanization of Mexicans here is evident, too. ''Mexican-Americans are much more American than they realize. They've gone to school in English and the border language (Spanish heavily laced with American words) is the toughest thing in the world to interpret from,'' he says.
And the best tangible example of border culture, Rice says, is ''cholos.'' Descendants of the '40s Zoot Suit phenomenon, cholos make up a Mexican-American cultural group distinguished by their clothing - bandannas, white T-shirts, and oversize chinos folded into pleats at the waist and tied with string.
''The average American sees this as a Mexican phenomenon,'' he explains. ''The Mexican sees it as American. But it is Mexican-American.''