Tripitaka is a historical reference in Book One (Awake to Emptiness) of The Years of Rice and Salt.

According to http://www.godchecker.com/pantheon/chinese-mythology.php?deity=TRIPITAKA

TRIPITAKA: The famous Tang Dynasty Buddhist monk who travelled to India to fetch scriptures in the company of MONKEY, PIGSY and SANDY.

Chinese Mythology:

Although Buddhism had achieved a foothold in China, knowledge of its more profound mysteries was scarce. The minor (Little Vehicle) Scriptures were constantly consulted, but these were pretty tame and hardly anything to get excited about. Only the Big Vehicle Scriptures could truly save the damned.

BUDDHA was well aware of this little problem, and asked GUAN-YIN to help. "I have three full baskets of Scripture on Earth, waiting at the Temple of the Thunderclap for someone to collect them," he said. "Could you find a pilgrim to travel the hundred thousand leagues from China to India and back?"

"Of course," he mused thoughtfully, "I could just transport them there myself in an instant, but the Chinese people just wouldn't appreciate it."

So GUAN-YIN travelled down to Earth, looking for a humble and pious Chinese monk. Preferably one with stout legs. And a young priest named Xuan Zang seemed to fit the bill perfectly, so with a modest display of holy fireworks, GUAN-YIN persuaded the Emperor to send him on the quest.

In honor of his mission, Xuan adopted the name TRIPITAKA (which means 'Three Baskets' in Sanskrit). And off he went on the dangerous and incredibly long journey to India, taking only a horse, a change of underwear and a golden begging bowl.

Now TRIPITAKA, being young and foolish, was probably the least likely hero imaginable. When faced with danger he was liable to fiddle with joss sticks and burst into tears. Luckily GUAN-YIN had provided backup in the form of MONKEY, PIGSY and SANDY. They were not a well-knit team, and argued constantly, but in the course of time TRIPITAKA's disciples became used to his silly human ways and fought tooth and nail to protect him.

The four travellers (plus horse) negotiated their way through eighty-one disasters and many exciting adventures before arriving, many years later, at the Temple of the Thunderclap. Achieving enlightenment, TRIPITAKA passed into Buddhist Heaven with much ceremonial hoo-hah and prepared to fulfill his mission. So he was somewhat disconcerted when ANANDA and KASYAPA tried to fob him off with blank scrolls.

BUDDHA was somewhat peeved. "Such knowledge is infinitely precious, and not to be given away lightly. Everything has its price, even in Heaven," he said. "Give them your golden begging bowl as payment and we'll call it a deal. Although," he added, "to be perfectly honest, those blank scrolls are actually far more illuminating than the real ones."

Convincing BUDDHA that the Chinese people would much prefer scriptures with writing on, TRIPITAKA handed over his bowl, collected five thousand and forty-eight precious scrolls and headed back to China, taking the illuminated Buddhist Express which got him there in double-quick time.

And so at last his mission was fulfilled. He now takes his place in Buddhist Heaven and is known as the 'Buddha of Precocious Merit'.

References
In The Years of Rice and Salt Tripitaka is refered to on page one of Book One at the top of the page where Robinson is telling the audience that monkey never dies and has continously come back to help in times of trouble. He then cites a specific example saying that Monkey helped "Tripitaka through the dangers of the first journey to the west, to bring Buddhism back from India to China". This is a historical reference to the Chinese form of Tripitaka that is sometimes used as a honorable title for a Buddhist monk who mastered all the Tripitaka canons. In Book One where Robinson uses the word Tripitaka he is specifically refering to to Xuanzang, the Tang Dynasty monk, who pilgrimaged to study Buddhism in India and bring back Buddhist text to China. Robinson uses this historical reference in order to incorporate Buddhist religious beliefs into the context of the story, as well as use it to began his story of the influence of the "East" on the rest of the world, and uses a historical reference to do it. He begans with a historical reference to start his telling of an alternative history.