The Proposal co-stars, who were also seen on a hiking excursion in the area, were joined by two others, as well as the actress's 1-year-old son Louis, for what was described as a "really informal" meal, People reports.
"They didn't seem like they were a couple," a source said. "It was very relaxed, totally friendly. She wasn't romantic with anyone at the table."
Bullock and Reynolds were rumoured to be dating after spending New Year's Eve together, but the actress later laughed off the reports.
"I think there will be a collective sigh amongst women across the United States when I say he is not my lover!" Bullock told the Today Show's Al Roker in January.
Last year, Bullock divorced the CEO of West Coast Choppers Jesse James after reports of his infidelity surfaced.
James has since become engaged to LA Ink star Kat Von D. The couple cancelled their forthcoming nuptials last month, but reconciled earlier this week.