>> Thompson: ON THIS EDITION FOR SATURDAY, NOVEMBER 24: SPAIN REACHES A DEAL WITH THE U.K. ON THE EVE OF THE BREXIT SUMMIT; ACCELERATING DRUG DISCOVERIES WITH A "BODY ON A CHIP"; AND RAPID RESPONSE MUSEUMS COLLECTING ARTIFACTS DOCUMENTING REAL-TIME EVENTS.

NEXT ON PBS NEWSHOUR WEEKEND.

FROM THE TISCH WNET STUDIOS AT LINCOLN CENTER IN NEW YORK, MEGAN THOMPSON.

>> Thompson: GOOD EVENING, AND THANK YOU FOR JOINING US.

AFTER 17 MONTHS OF NEGOTIATIONS, THE EUROPEAN UNION IS CLOSE TO AN AGREEMENT THAT WOULD PAVE THE WAY FOR A BRITISH EXIT FROM THE POLITICAL AND ECONOMIC BODY.

AS BRITISH PRIME MINISTER THERESA MAY HEADED TO BRUSSELS FOR A SPECIAL BREXIT SUMMIT TOMORROW, THE EUROPEAN COUNCIL PRESIDENT, DONALD TUSK, TWEETED AN ENDORSEMENT OF THE DEAL.

TUSK WROTE: THIS COMES AFTER THE SPANISH PRIME MINISTER THREATENED TO VETO THE BREXIT DEAL OVER THE DISPUTED BRITISH TERRITORY OF GIBRALTAR, LOCATED IN THE SOUTH OF SPAIN.

SPAIN LIFTED ITS OBJECTIONS AFTER A LAST-MINUTE AGREEMENT WITH THE U.K.

IF THE CURRENT BREXIT DEAL IS PASSED IN BRUSSELS, PRIME MINISTER THERESA MAY WILL STILL HAVE TO WIN SUPPORT FROM BRITAIN'S PARLIAMENT, WHERE, SO FAR, A MAJORITY REMAINS OPPOSED TO THE NEGOTIATED TERMS.

THOUSANDS OF DEMONSTRATORS, ANGRY AT RISING FUEL TAXES, AGAIN TOOK TO THE STREETS IN PARIS AND ACROSS FRANCE TODAY.

IT'S THE SECOND WEEKEND THAT PROTESTERS BLOCKED ROADS AND BURNED BARRICADES AS THEY CLASHED WITH FRENCH SECURITY FORCES.

POLICE FIRED TEAR GAS AND SPRAYED WATER CANNONS ON THE DEMONSTRATORS.

AUTHORITIES SAY AT LEAST EIGHT PEOPLE WERE INJURED IN TODAY'S PROTESTS, INCLUDING TWO POLICE OFFICERS.

FRENCH PRESIDENT EMMANUEL MACRON IMPOSED THE NEW TAXES AS PART OF A PLAN TO LESSEN DEPENDENCE ON FOSSIL FUELS AND FUND RENEWABLE ENERGY INVESTMENTS.

MORE THAN A DOZEN PEOPLE HAVE DIED IN HAITI DURING A WEEK OF ANTI-GOVERNMENT DEMONSTRATIONS AND POLITICAL UNREST.

POLICE FIRED TEAR GAS INTO CROWDS OF PROTESTERS YESTERDAY.

MANY ARE DEMANDING HAITIAN PRESIDENT JOVENEL MOISE STEP DOWN, ACCUSING HIM OF NOT INVESTIGATING CORRUPTION ALLEGATIONS AGAINST THE PREVIOUS ADMINISTRATION.

AT LEAST 11 PEOPLE DIED IN THE PROTESTS AND SEVERAL OTHERS WERE KILLED WHEN A GOVERNMENT CAR LOST A WHEEL AND PLOWED INTO A CROWD.

THE VIOLENT PROTESTS HAVE PARALYZED COMMERCE IN HAITI'S CAPITAL OF PORT-AU-PRINCE AND FORCED SCHOOLS AND SHOPS TO REMAIN CLOSED.

MEXICAN OFFICIALS ARE DENYING A "WASHINGTON POST" REPORT THAT THERE IS A DEAL TO KEEP ASYLUM SEEKERS IN MEXICO WHILE THEIR CLAIMS MOVE THROUGH U.S. COURTS.

IN AN INTERVIEW WITH THE "POST," MEXICO'S INCOMING INTERIOR MINISTER SAID THE COUNTRY'S NEW GOVERNMENT HAS NEGOTIATED A "REMAIN IN MEXICO" POLICY WITH THE TRUMP ADMINISTRATION, WHICH WOULD CHANGE LONG-STANDING RULES FOR ASYLUM SEEKERS.

THE NEWS COMES JUST A DAY AFTER THE MAYOR OF TIJUANA DECLARED A HUMANITARIAN CRISIS AND ASKED THE UNITED NATIONS FOR HELP TO DEAL WITH APPROXIMATELY 5,000 MIGRANTS FROM THE SO-CALLED CENTRAL AMERICAN CARAVAN NOW GATHERED IN THE BORDER CITY.

THE DEADLY WILDFIRE IN NORTHERN CALIFORNIA IS NOW ALMOST COMPLETELY CONTAINED THANKS TO SEVERAL DAYS OF HEAVY RAIN, BUT THE SEARCH FOR HUMAN REMAINS CONTINUES THROUGH NOW MUDDY ASH AND DEBRIS.

AT LEAST 84 PEOPLE DIED IN THE TWO-WEEK BLAZE, AND MORE THAN 500 REMAIN UNACCOUNTED FOR.

IN SOUTHERN CALIFORNIA, MORE RESIDENTS WERE ALLOWED TO RETURN TO AREAS PREVIOUSLY EVACUATED BECAUSE OF THE WOOLSEY FIRE.

CREWS CONTINUE TO REPAIR POWER AND OTHER UTILITIES IN THE AREA, WITH MORE THAN 1,000 PEOPLE STILL UNDER EVACUATION ORDERS, DOWN FROM 250,000 AT THE HEIGHT OF THE FIRE.

>> Thompson: HUNDREDS OF VOLUNTEERS ON THANKSGIVING DAY HELPED THOSE DISPLACED BY THE CALIFORNIA FIRES HAVE A FEAST.

READ ABOUT IT ON OUR WEB SITE AT www.pbs.org/newshour.

>> Thompson: WHAT IF WE COULD TEST NEW DRUGS WITHOUT HUMAN AND ANIMAL TRIALS?

AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY, RESEARCHERS HAVE DEVELOPED WHAT IS BEING CALLED THE "BODY ON A CHIP," A DEVICE ROUGHLY THE SIZE OF A PAPERBACK BOOK THAT MAY DO JUST THAT.

HARI SREENIVASAN RECENTLY SPOKE WITH M.I.T.

PROFESSOR LINDA GRIFFITH, WHO IS LEADING THE TEAM DEVELOPING THIS NEW TECHNOLOGY.

SHE JOINED HIM VIA SKYPE FROM CAMBRIDGE, MASSACHUSETTS.

>> Sreenivasan: FIRST, EXPLAIN HOW IT WOULD WORK.

>> SO, IF YOU WANT TO STUDY A DISEASE-- FOR EXAMPLE, THE DISEASE IS AFFECTING THREE ORGANS IN THE BODY-- YOU WOULD BUILD A MODEL OF THAT AND THEN BUILD AN EXPERIMENT THAT REPRESENTS THAT USING HUMAN CELLS AND COMPONENTS.

>> Sreenivasan: SO, THESE ARE ON A CELLULAR LEVEL MIMICKING WHAT A PARTICULAR ORGAN THAT I WOULD HAVE DOES?

>> ACTUALLY, EVEN BETTER THAN THAT, BECAUSE WE BUILD A LITTLE MODEL OF THAT ORGAN, OR AT LEAST PARTS OF THAT ORGAN.

SO, YOUR ORGANS HAVE BILLIONS AND BILLIONS OF CELLS.

WE COMBINE MANY DIFFERENT KINDS OF CELLS FROM EACH ORGAN TOGETHER IN A 3D MODEL.

THEN, WE CONNECT THEM TOGETHER SO THEY TALK TO EACH OTHER LIKE THEY WOULD IN THE BODY.

THIS IS REALLY IMPORTANT FOR THINGS LIKE ARTHRITIS, ALZHEIMER'S, WHERE YOU'VE GOT MULTIPLE ORGANS INVOLVED.

YOU NEED THEM TO BE A MODEL IN VITRO THAT'S HUMAN, TALKING TO EACH OTHER.

>> Sreenivasan: WHEN A NEW DRUG IS INTRODUCED, YOU CAN STUDY HOW IT MIGHT AFFECT MY LIVER AND MY PANCREAS AND MY BLADDER AT THE SAME TIME?

>> ABSOLUTELY.

WE RIGHT NOW ARE DOING GUT LIVER PANCREAS AND GUT LIVER BRAIN, BUT YOU'VE GOT THE IDEA.

AND PART OF IT IS NOT JUST TO SAY HOW WILL THE DRUG AFFECT THIS, BUT WE CAN EVEN SAY WHAT SHOULD THE DRUG EVEN BE?

BECAUSE RIGHT NOW, THE HARDEST THING IS TO FIGURE OUT WHAT KIND OF DRUG WILL BE GOOD FOR TREATING A COMPLICATED DISEASE.

>> Sreenivasan: HOW DO YOU ACCOUNT FOR HOW HUMAN BODIES HAVE IMMUNE SYSTEMS BUILT IN?

I MEAN, IT SEEMS LIKE OUR OWN BODIES SOMETIMES REJECT OR ACCEPT DRUGS BASED ON HOW WE'RE BUILT.

>> YES, ALMOST EVERY DISEASE THAT WE HAVE A DIFFICULT TIME SOLVING INVOLVES THE IMMUNE SYSTEM, AND THAT'S SO DIFFERENT IN HUMANS THAN IN MICE.

SO, OUR SYSTEM ACTUALLY HAS PART OF THE IMMUNE SYSTEM.

IT HAS SOME OF THE LIVER'S INNATE IMMUNE SYSTEM, THE GUT INNATE IMMUNE SYSTEM.

OTHER PARTS HAVE TO BE TRAINED, AND THIS IS MUCH HARDER TO DO.

WE HAVE A PROJECT WITH THE PHARMACEUTICAL COMPANY WHERE WE'RE DOING EXACTLY THAT.

AND THIS IS VERY EARLY STAGE, BUT THIS IS GOING TO HAPPEN IN THE FUTURE.

THIS IS WHERE THE WHOLE FIELD IS GOING, TO INCORPORATE THE IMMUNE SYSTEM SO WE CAN STUDY THESE REALLY COMPLICATED DISEASES, INCLUDING CANCER, ALZHEIMER'S, AND SO ON, THAT INVOLVE THE IMMUNE SYSTEM.

>> Sreenivasan: DOES THIS HELP BRING ABOUT THAT IDEA OF PERSONALIZED MEDICINE IN THE FUTURE?

I MEAN, COULD I ESSENTIALLY RUN ALMOST A CLINICAL TRIAL BASED ON MY OWN ORGANS IN MY OWN BODY AND SEE IF THIS DRUG IS RIGHT FOR ME VERSUS YOU?

>> SORT OF, MAYBE.

THE COST WOULD HAVE TO COME DOWN TO HAVE IT BE THAT PERSONAL.

BUT THINK ABOUT IT.

I STUDY A DISEASE CALLED ENDOMETRIOSIS.

ABOUT 10% OF WOMEN HAVE THIS.

WE PUBLISHED THE FIRST PAPER DOING A MOLECULAR CLASSIFICATION INTO A FEW GROUPS OF PATIENTS.

SO, YOU CAN IMAGINE MAYBE THERE'S TEN GROUPS OF PATIENTS, AND NOW YOU'LL FIGURE OUT HOW TO MAKE A DRUG FOR EACH OF THOSE TEN GROUPS.

AND THEN, WE'LL FIGURE OUT HOW DO WE TEST YOU SO THAT WE CAN SEE WHICH GROUP YOU FALL IN.

THEN, YOU CAN TAKE THE RIGHT DRUG WITHOUT US HAVING TO BUILD YOU BECAUSE BUILDING YOU IS A VERY PERSONAL THING.

>> Sreenivasan: AND IS THERE AN ACCELERATION IN THIS FIELD LIKE THERE IS IN COMPUTERS, MEANING DOES IT GET CHEAPER OVER TIME AND FASTER OVER TIME?

>> WE WOULD EXPECT THE ANALOGY TO HOLD.

YOU CAN IMAGINE, IT'S KIND OF LIKE BUILDING AN iPHONE.

AND TO MAKE THE iPHONE WORK, YOU HAD TO INVENT THE PHONOGRAPH, AND THEN THE CASSETTE TAPE PLAYER.

YOU HAD TO INVENT TELEVISION.

YOU HAD TO INVENT COMPUTERS.

SO, A LOT OF THINGS CAME TOGETHER.

THIS IS VERY SIMILAR.

THERE HAVE TO BE HUGE ADVANCES IN BIOLOGY, MATERIAL SCIENCE, AND, ACTUALLY, IN ENGINEERING, BECAUSE WE NEED ENGINEERS WHO THINK ABOUT HOW DO WE MODEL THE HUMAN BODY?

HOW DO WE THINK ABOUT INFORMATION FLOW AND DESIGN THESE SYSTEMS?

YOU'VE GOT TO BE ABLE TO DESIGN THEM BEFORE YOU BUILD THEM.

>> Sreenivasan: SO, HOW SOON UNTIL THIS IS OUT IN THE WILD, SO TO SPEAK?

>> SOME PARTS ARE GOING OUT IN THE WILD, IF YOU COUNT, LIKE, AMGEN OR OTHER PEOPLE WE WORK WITH "THE WILD."

IT'S GOING, AGAIN, TO BE SORT OF LIKE THE CELL PHONE BECAUSE THE INDIVIDUAL ELEMENTS THAT ARE NEEDED TO MAKE IT HAPPEN ARE ALL MOVING QUICKLY IN PARALLEL AND STARTING TO COME TOGETHER.

>> Sreenivasan: LINDA GRIFFITH OF M.I.T., THANKS SO MUCH FOR JOINING US.

>> THANK YOU FOR HAVING ME.

>> Thompson: FROM POLITICS TO PROTESTS, EVENTS SEEM TO UNFOLD SO QUICKLY THESE DAYS THAT IT CAN BE HARD TO KEEP TRACK OF THEM, LET ALONE PUT THEM IN PERSPECTIVE.

IN AN ATTEMPT TO TACKLE THOSE CHALLENGES, SOME MUSEUMS AND ARCHIVISTS ARE NOW TRYING TO CREATE A RECORD OF OUR TURBULENT ERA FOR FUTURE GENERATIONS BY GOING OUT INTO THE FIELD AND COLLECTING ARTIFACTS IN REAL TIME.

NEWSHOUR WEEKEND'S IVETTE FELICIANO HAS THE STORY.

>> Reporter: THIS IS THE NATIONAL MUSEUM OF AFRICAN-AMERICAN HISTORY AND CULTURE IN WASHINGTON, D.C.

HERE, DECADES-OLD ARTIFACTS AND PHOTOS FROM THE CIVIL RIGHTS ERA ARE DISPLAYED ALONG OBJECTS DEPICTING A MORE RECENT STRUGGLE.

LONNIE BUNCH IS THE MUSEUM'S FOUNDING DIRECTOR.

>> THIS IS A PHOTO OF FERGUSON AND DEMONSTRATIONS AROUND FERGUSON.

AND WHAT I THINK IS POWERFUL IS THAT MAYBE 20 YEARS AGO, WE MIGHT NOT HAVE COLLECTED THIS.

>> Reporter: THE PHOTO WAS TAKEN DURING THE PROTESTS OF THE 2014 POLICE KILLING OF MICHAEL BROWN.

IT WAS ACQUIRED BY THE MUSEUM AS PART OF WHAT IT CALLS ITS "RAPID RESPONSE COLLECTION PROGRAM."

WHEN MAJOR EVENTS UNFOLD, THE MUSEUM SENDS CURATORS INTO THE FIELD TO COLLECT ARTIFACTS.

THE IDEA IS TO CREATE A RECORD WELL BEFORE THE HISTORY BOOKS ARE WRITTEN.

>> SO, THE GOAL HERE IS NOT TO SORT OF SWEEP IN AND PICK UP EVERYTHING.

THE GOAL IS TO HAVE A FEW CENTRAL ARTIFACTS THAT GIVE YOU MANY MEANINGS; THAT ALLOW YOU TO SORT OF SAY IF SOMEBODY SEES THAT... FOR EXAMPLE, IF SOMEBODY SEES A SHIRT THAT SAYS, "BLACK LIVES MATTER," WE KNOW WHAT THAT MEANS TODAY, HOW IMPORTANT IT IS, BUT THEY MAY NOT KNOW THAT 20 YEARS FROM NOW.

SO, TO BE ABLE TO HAVE SOMETHING CLEAR AND CONCISE THAT WE CAN BUILD STORIES AROUND IS WHAT I ASK THE CURATORS TO COLLECT.

>> Reporter: OTHER ITEMS FROM FERGUSON IN THE MUSEUM'S COLLECTION INCLUDE THIS GAS MASK WORN BY A DEMONSTRATOR AND THIS SUIT WORN BY A PASTOR WHO ATTENDED THE PROTESTS.

ALSO COLLECTED BY MUSEUM CURATORS IN 2014, THIS T-SHIRT WORN BY A DEMONSTRATOR PROTESTING THE POLICE KILLING OF ERIC GARNER IN STATEN ISLAND, NEW YORK.

IN 2015, THIS RAKE WAS USED TO CLEAN UP A BALTIMORE NEIGHBORHOOD AFTER PEOPLE TOOK TO THE STREETS TO PROTEST THE DEATH OF FREDDIE GREY WHILE HE WAS IN POLICE CUSTODY.

THIS T-SHIRT DISPLAYS THE LOGO OF AN ANTI-VIOLENCE GROUP THAT FORMED AS A RESULT OF THE PROTESTS.

AND THIS BLACK PANTHER PIN WAS COLLECTED LATER THAT SAME YEAR FROM THE 20th ANNIVERSARY OF THE MILLION MAN MARCH IN WASHINGTON.

WHY IS RAPID RESPONSE COLLECTING IMPORTANT TO THE MISSION OF THIS CENTER?

>> IN SOME WAYS, ONE OF THE GREAT DIVIDES IN AMERICA'S ALWAYS BEEN RACE AND THAT AS AMERICANS GRAPPLE WITH THE CHANGING SENSE OF WHO THEY ARE, AS THEY GRAPPLE WITH THE CHANGING NOTIONS OF HOW RACE MATTERS AND PLAYS OUT, WE THOUGHT IT WAS REALLY IMPORTANT TO CAPTURE THOSE MOMENTS THAT WERE TRANSFORMATIVE.

I'LL BE HONEST, SOMETIMES YOU GUESS.

YOU SAY, "IS THIS GOING TO BE IMPORTANT OR NOT?"

FOR US, IT'S REALLY IMPORTANT THAT THIS MUSEUM, WHICH REALLY HAS TO HELP THE AMERICAN PUBLIC GRAPPLE WITH THINGS THAT HAVE DIVIDED US, TO NOT JUST BE ABOUT YESTERDAY BUT TO BE ABOUT AS MUCH ABOUT TODAY AND TOMORROW.

>> Reporter: YOU KNOW, TO PLAY DEVIL'S ADVOCATE, ARE YOU SHAPING HISTORY?

>> OF COURSE.

THE JOB OF A SCHOLAR IS TO BOTH LOOK BACK, MAKE SURE YOU INTERPRET THE PAST THROUGH DIFFERENT LENSES; BUT ALSO, IN A MUSEUM, YOUR JOB IS TO MAKE SURE THE NEXT GENERATION CAN INTERPRET THE WORLD YOU LIVE IN TODAY.

SO, THE KINDS OF THINGS YOU COLLECT ARE SHAPING HISTORY, SHAPING THE WAY PEOPLE INTERPRET HISTORY.

I KNOW, AS A SCHOLAR OF AFRICAN AMERICAN HISTORY, THERE WERE MANY TIMES I WANTED TO DO EXHIBITIONS, AND THERE WAS NOTHING IN THE COLLECTIONS THAT COULD TELL THOSE STORIES.

THAT SHAPES HISTORY BY OMISSION.

SO, THE NOTION FOR ME IS, LET'S GIVE PEOPLE AS MANY OPPORTUNITIES AS POSSIBLE.

THEY MAY DECIDE THAT THE STORIES WE'VE COLLECTED AREN'T THAT IMPORTANT, AND THAT'S FINE.

BUT I WANT TO MAKE SURE THAT YOU'VE GOT THE RESOURCES TO BE ABLE TO TELL IMPORTANT STORIES IN THE FUTURE.

>> Reporter: OTHER INSTITUTIONS USE RAPID RESPONSE COLLECTION, AS WELL.

THE NEW YORK HISTORICAL SOCIETY BEGAN SENDING OUT "HISTORY BRIGADES" AFTER THE SEPTEMBER 11 TERRORIST ATTACK IN 2001, AND IT HAS COLLECTED ITEMS COMMEMORATING THE 2017 AND 2018 WOMEN'S MARCHES ON WASHINGTON.

IN ORLANDO, FLORIDA, THE ORANGE COUNTY REGIONAL HISTORY CENTER ACQUIRED MORE THAN 7,000 ITEMS FOR ITS "ONE ORLANDO" COLLECTION.

THE COLLECTION REVOLVES AROUND THE 2015 PULSE NIGHTCLUB SHOOTING.

AND THE NATIONAL CIVIL RIGHTS MUSEUM IN MEMPHIS, TENNESSEE, HAS AN EXHIBIT ON THE TRUMP ADMINISTRATION'S IMMIGRANT FAMILY SEPARATION POLICY.

THE EXHIBIT IS TITLED "I AM A CHILD."

IT WAS INSPIRED BY THE ICONIC "I AM A MAN" PHOTOS TAKEN DURING THE 1968 MEMPHIS SANITATION WORKERS STRIKE.

THE EXHIBIT USES PHOTOGRAPHS THAT WENT VIRAL ON SOCIAL MEDIA EARLIER THIS YEAR.

THEY SHOW CHILDREN PROTESTING ON THE STEPS OF THE IMMIGRATION AND CUSTOMS ENFORCEMENT AGENCY'S NEW YORK OFFICE.

>> I THINK WHENEVER AMERICA IS REALLY DEBATING ITS IDENTITY, DEBATING WHO IT IS, GRAPPLING WITH ISSUES THAT DIVIDE US, THAT'S WHEN A MUSEUM OUGHT TO BE MORE AGGRESSIVE AND COLLECT MATERIAL.

IT JUST SEEMS TO ME THAT A GOOD MUSEUM ISN'T JUST A PLACE OF NOSTALGIA.

IT'S NOT JUST A PLACE OF THE EXOTIC.

IT'S A PLACE THAT PROVIDES PEOPLE USEFUL TOOLS TO GRAPPLE WITH THE WORLD THEY FACE.

AND BY GRAPPLING WITH THE WORLD THEY FACE, THEY CAN MAKE IT BETTER.

>> Thompson: IN ARIZONA, EXPERIENCED CAVERS AND VOLUNTEERS HAVE BEEN WORKING ON ONE OF THE LARGEST GRAFFITI REMOVAL PROJECTS IN THE U.S. FOREST SYSTEM.

IT'S THE LATEST RESTORATION EFFORT FOR PEPPERSAUCE CAVE IN THE CORONADO NATIONAL FOREST, JUST NORTH OF TUCSON.

THE POPULAR CAVE HAS MORE THAN 7,300 FEET OF PASSAGES AND IS ONE OF THE FEW CAVES IN ARIZONA OPEN TO VISITORS BOTH DAY AND NIGHT.

THE CLEAN-UP AND RESTORATION IS PART OF A MULTI-YEAR, MULTI- PHASE PROJECT.

OUR PARTNERS AT ARIZONA PUBLIC MEDIA HAVE THE STORY.

>> THIS BOX IS GOING ALL BEYOND THE RABBIT HOLE.

I'M GOING TO START ON DRILLS AND GRINDERS, OKAY?

I'M RAY KEELER.

I'M THE PRESIDENT OF THE CENTRAL ARIZONA GROTTO.

IT'S THE LOCAL CHAPTER OF THE NATIONAL SPELEOLOGICAL SOCIETY.

WE'RE ABOUT CAVE EXPLORATION CONSERVATION SCIENCE AND JUST A BETTER UNDERSTANDING OF THE CAVES.

TODAY, WE ARE DOING...

STARTING A THREE-DAY EFFORT.

FRIDAY IS SET-UP; SATURDAY, THEY'LL BE ABOUT 20 PEOPLE HERE ALL DAY CLEANING TAGS; AND SUNDAY, WE'LL WORK TILL NOON AND THEN BRING ALL THE EQUIPMENT OUT OF THE CAVE.

IN WE GO.

LET'S DO IT.

THE SIGN OUTSIDE HAS FOUR RULES: NO SPRAY PAINT; PEE BEFORE YOU GO INTO THE CAVE; HAVE AT LEAST ONE LIGHT PER PERSON; AND THEN TAKE YOUR TRASH OUT WITH YOU.

THE SECOND ROOM WAS MOST... ONE OF THE MOST GRAFFITIED ROOMS IN THE ENTIRE CAVE-- REDS, YELLOWS, GREENS, BLUES, BLACKS, WHITES, NAMES, SYMBOLS.

THIS ROOM HERE HAD ANOTHER 30 TO 40 TAGS ON THIS WALL, AND THAT WALL THERE ARE ANOTHER 40 OR 50.

AND THAT PASSAGE HERE, IT'S A CRAWL-THROUGH.

SO, WITH ALL THE TEAMS WORKING, WE JUST KEEP PROGRESSING INTO THE CAVE.

WHEN WE GOT HERE, THERE WERE FIVE OR SIX SPRAY-PAINT TAGS WITH LOTS OF COLORS.

WE'VE CLEANED THOSE OFF 25 OR 30 TAGS ON THIS SIDE THAT WENT CLEAR IN HERE, THROUGH... BACK INTO THIS PASSAGE, AND THEN ANOTHER 50 SCRATCHES ALONG THIS WALL.

IT WAS BAD, AND WE'VE CLEANED IT ALL OUT.

THAT WAS THREE PEOPLE FOR THREE HOURS TO DO THIS.

SOMEBODY WANTS TO LEAVE THEIR MARK, SAME AS 40,000 YEARS AGO, ONLY THEY HAVE SPRAY PAINT AND STABLE LIGHTS.

THIS IS FLAT-OUT UNNECESSARY VANDALISM.

>> THE DRAW FOR ME IS... IS THE WORK.

I DO A LOT OF CONSERVATION WORK.

THIS ISN'T THE ONLY CAVE I DO.

IT'S TOUGH WHEN YOU GOT TO CLEAN UP ON OTHER PEOPLE'S STUFF.

IT'S BAD ENOUGH CLEANING UP OUR OWN STUFF, AND WE TRY TO BE VERY, VERY CAREFUL SO WE DON'T LEAVE EVEN BREAD CRUMBS ON THE GROUND.

SO, WHEN THEY HAVE TO DO IT FOR OTHER PEOPLE, YOU KNOW, IT'S...

IT'S TOUGH, BUT IT'S WHAT WE DO BECAUSE WE WANT TO KEEP OUR ENVIRONMENT.

>> I PARTICIPATE IN THIS PROJECT BECAUSE I THINK CAVES ARE ONE OF THE LAST PLACES ON EARTH THAT ARE REALLY SOMETHING SPECIAL, REALLY UNEXPLORED.

IT'S SOMETHING THAT MOST PEOPLE NEVER GET A CHANCE TO SEE ANYTHING SO OUT OF THE ORDINARY.

AND THIS CAVE, IT'S GREAT BECAUSE IT'S REALLY ACCESSIBLE.

A LOT OF PEOPLE FROM TUCSON, FROM ALL OVER THE PLACE CAN COME HERE AND REALLY SEE WHAT CAVING IS ALL ABOUT.

BUT, UNFORTUNATELY, YOU KNOW, OVER THE YEARS, PEOPLE HAVE DECIDED TO VANDALIZE IT.

>> WE PUT IN REFLECTIVE ARROWS SO YOU CAN SEE ONE TO THE NEXT.

AND IF YOU MISS THAT ONE, WE'VE GOT ANOTHER ONE POINTING TO THE RIGHT.

SO, THIS ONE'S POINTING DOWN UNDERNEATH, AND THAT ONE'S TO THE RIGHT.

THE IDEA IS TO MAKE SURE PEOPLE CAN GET OUT THE EASIEST WAY OF THE CAVE.

PEOPLE WERE PUTTING IN ARROWS THEMSELVES.

SOME PEOPLE MARK THEIR ARROWS GOING INTO THE CAVE.

WE WENT THIS WAY.

INSTEAD, SOME PEOPLE MARK THE ARROWS GOING THE OPPOSITE DIRECTION.

SO, SOMETIMES THE ARROWS ARE POINTING IN, SOME ARE POINTING OUT.

SO, NOW, THEY WERE DOING MULTIPLE TAGS, MULTIPLE ARROWS, WITH DIFFERENT COLORS, SO YOU HAVE YOUR OWN COLOR.

WE'VE SOLVED ALL THAT.

WE'VE MADE IT EASIER.

THERE'S NO NEED FOR IT ANYMORE.

>> I'M FROM NEW YORK CITY.

I LIVE IN HARLEM.

I'M HERE WITH SOME FAMILY, FRIENDS.

THEY TOOK ME TO THE CAVE, AND I GUESS IS THE WORD "SPELUNKING"?

BECAUSE WE'RE... WE'RE GOING AROUND IN THE CAVE, AND WE'RE JUST CLIMBING ALL THROUGH AND EXPLORING EVERYTHING.

IT'S BEEN COMPLETELY AMAZING.

I HAVE NEVER DONE ANYTHING LIKE THIS BEFORE, AND I HAD NO IDEA WHAT TO EXPECT.

IT'S BEEN A LOT OF FUN.

>> I REALLY THINK, LIKE, THINGS LIKE THIS, LIKE, VOLUNTEER WORK FOR, LIKE, NATURAL AREAS ARE JUST, LIKE, PHENOMENAL PEOPLE.

AND, YOU KNOW, SOMEONE'S GOT TO DO IT.

AND IT'S...

IT'S GRUELING WORK, AND IT'S...

I RESPECT PEOPLE THAT... THAT TAKE THEIR TIME TO DO THAT.

>> WE ENJOY CAVES, SO THIS IS JUST OUR WAY OF PAYING BACK TO THE COMMUNITY AND TO THE FOREST SERVICE FOR ALLOWING US THE OPPORTUNITY TO GO INTO CAVES.

>> SOLVENT DRILLS, SOLVENT DRILL, BRUSH, BRUSH, BRUSH, SOLVENT.

AND WE GOT IT TO A POINT WHERE IT'S BEEN MUDDED OVER, BUT... >> AND UNLESS YOU LITERALLY GO BEHIND THE FORMATION AND PUT YOUR HEAD DOWN OR JUST LOOK AT THE WATER, YOU DON'T REALIZE THERE'S AIR BLOWING OUT.

YOU BLEED, YOU SWEAT, YOU GET DUST EVERYWHERE AND, LIKE... OR MUD.

AND JUST, LIKE, YOU HAVE GOOD TIMES AND YOU HAVE BAD TIMES.

BUT, AT THE END, YOU COME OUT AND YOU LAUGH AND YOU JUST, LIKE, "THIS IS WHAT WE DID."

LIKE, "WE DID THIS."

CAVERS, WE DO THIS ON OUR SPARE TIME.

WE'RE ALL VOLUNTEERS.

NONE OF US GET PAID.

>> THE REASON WE WERE DOING THIS IS BECAUSE PEOPLE GO THROUGH THE CAVE, AND THEY SAY, "SOMEBODY SHOULD TAKE CARE OF THAT GRAFFITI.

SOMEBODY SHOULD DO SOME OF THAT."

AND WE DECIDED WE WERE GOING TO BE THE SOMEBODY.

>> Thompson: FINALLY TONIGHT, IT'S BEEN MORE THAN SIX WEEKS SINCE HURRICANE MICHAEL HIT THE FLORIDA PANHANDLE, LEAVING THOUSANDS HOMELESS.

JOIN US TOMORROW FOR A SPECIAL REPORT ON "FLORIDA'S FORGOTTEN COAST," WHERE SOME RESIDENTS SPENT THANKSGIVING IN SHELTERS AND MAKESHIFT HOMES STILL WAITING FOR WORD ON WHEN AND HOW THEY CAN REBUILD.

THAT'S ALL FOR THIS EDITION OF PBS NEWSHOUR WEEKEND.

I'M MEGAN THOMPSON.

THANKS FOR WATCHING.

HAVE A GOOD NIGHT.