U.S. Customs and Border Protection solicited bids a year ago using existing border security funding to build eight wall prototypes and awarded contracts to six private companies for mock-ups that are each 30 feet long and as much as 30 feet high.
Trump's solo flight suggests the political risk he brings to state Republicans given his low popularity in California.
Trump, making his first trip to California as president, said he preferred a fully concrete wall because it was the hardest to climb, but he noted that it needed to be see-through. Kevin Faulconer said a popular cross-border airport terminal connecting San Diego and Tijuana shows that "building bridges has worked wonders". She said the arrests of more than 150 people were "intended exclusively to terrorize innocent immigrant families".
"If you didn't have walls over here, you wouldn't even have a country", Trump said. "No wall!" near the San Ysidro crossing, where tens of thousands of people enter the US daily from Tijuana, Mexico, many on their way to work or school in San Diego.
Mr Trump also slammed Mr Brown for high state taxes, saying Mr Brown "has done a very poor job running California". And while some critics have organized rallies elsewhere to avoid a clash, counter-protesters are anticipated to make an appearance as well. The Justice Department recently sued over state laws that limit co-operation with immigration authorities, which state officials have harshly criticized.
California has emerged as an epicenter of opposition to Trump's immigration policies.
Trump's tour of the sample wall sections at Otay Mesa Port of Entry stirred plans for protests in a state where the project is deeply unpopular, as is the president.
But Trump seemed optimistic that a change in leadership following the Mexican election in July could lead to a more favorable set of circumstances.
UPDATED with LAPD traffic advisory, 2:05 PM: Donald Trump's first trip to California since being elected president has been shrouded in secrecy - at least the Los Angeles portion of it. Trump is scheduled to visit eight prototypes for the massive wall he wants built along the USA border with Mexico. Protests had already broken out there a day ahead of Trump's arrival and a similar scene of uproar could unfold later in the day when he arrives to Los Angeles. But U.S. and Mexican authorities appeared to be collaborating closely on security measures for the president's visit. On the Mexican side, federal and state police stood by.
Trump's visit comes just days after his Justice Department sued to block California laws created to protect people living in the US illegally.
Mr Trump has asked the US Congress for $18 billion to build the structure, but the funding has become ensnared in controversy over a host of immigration restrictions he and Republicans have proposed.
The Justice Department last week sued to block a trio of California laws created to protect people living in the US illegally. Trump has insisted Mexico pay for the wall. But, he said, "I have to do it".
Jeff Schwilk, founder of San Diegans for Secure Borders and organiser of a pro-Trump rally, the city resolution does not reflect the views of many residents, who feel the border is not secure.
Throughout the president's visit to the border, protesters and journalists watched from rooftops on the Mexican side of the existing border fence - under the watchful eye of police on both sides.
Security is sure to be tight, although it is unknown to what extent Trump might expose himself in examining the prototypes.
San Diego's city council a year ago passed a resolution opposing Trump's proposed wall. "It's something that he's going to continue to push for".