LOS ANGELES — Most Californians with an urge to smoke a joint will enter the state’s legal marijuana marketplace through a single doorway — at a retail shop.

But out of view of those day-to-day sales, the state is ushering in a sprawling, untested system to move pot from place to place that will also serve as a collection point for taxes, a gateway for testing and a packaging center for the plant’s fragrant buds.

The so-called marijuana distributor is a kind of skeleton connecting the state’s emerging industry of growers, sellers and manufacturers. It’s envisioned as a vast back office where the grunt work of keeping track of cannabis and getting it from farms to store shelves will take place.

But just days after legal sales began, there are concerns that not enough companies are licensed and ready to transport pot. Some predict that within weeks, cannabis could be marooned at warehouses while shelves go barren.

“There’s going to be huge bottleneck in the distribution network in California at some point,” said part-owner of a marijuana distribution company. Billions of dollars of pot will need to move through the market in 2018, and “I don’t believe there are enough businesses to handle it,” he said.

Flow Kana CEO Michael Steinmetz, whose company distributes cannabis products from small, outdoor farmers, said a slow rollout of licenses has resulted in a limited pool of distributors.

A patchwork of rules has emerged so far, with some cities allowing legal sales and others banning all commercial pot activity. Los Angeles — the state’s biggest market — has yet to authorize any licenses, though the first could be issued next week.

Kana Flow, which is developing a new distribution center on the site of a former winery, transports cannabis for about 100 local producers. While many retailers stocked up in advance of legal sales, “I do think we are going to see a big reduction in supply,” Steinmetz predicted.

A crimp in the supply chain, if it happens, would reprise what occurred in Nevada last year, when the start of legal sales saw a surge in demand with too few licenses to distribute it.

Pot distribution in California has long been an informal and largely hidden business, with arrangements made between growers and sellers. The move to the new system will be a major transformation: Under California law, pot can be transported only by companies holding a distributor license.

In the past, “it was all trust and handshakes,” Los Angeles dispensary owner Jerred Kiloh said. “Growers would drive it down in their Toyota Tacoma.”

California’s top pot regulator, Lori Ajax, said in an interview last month that a decision to make distributor licenses broadly available should help keep pot moving from farms to storefronts.

The uncertainty surrounding the distribution pipeline is just one question mark as California attempts to transform its long-standing medicinal and illegal marijuana markets into a multibillion-dollar regulated system.