The S&P 500 declined 0.4% to 2,058.38 in midday trading.
The Dow Jones Industrial Average declined 0.5% to 17,693.75 and the Nasdaq declined 0.6% to 4,868.73.
The yield on a 10-year Treasury bond fell 3.6% to 1.86%.
The price of gold rose 2.1% to $1,208.
Newport Beach-based Clean Energy Fuels Corp. was up 3.5% to $5.52 and a $499 million market cap. The natural gas fueling station operator said Jacksonville, Fla.-based Raven Transport Co. Inc. would fuel an additional 115 trucks that run on liquefied natural gas at Clean Energy facilities in the Southeast.
Anaheim-based Willdan Group Inc. was down 12% to $13.92 and a $106 million market cap. The engineering company yesterday reported higher revenue and earnings for its fourth quarter and full year compared with the same periods last year, but said costs for each period grew by about one-third, as well.
Santa Ana-based Greenwood Hall Inc. was up 5.3% to 79 cents and a $35 million market cap. The education services provider said it hired New York City-based Berenson & Co. to help it identify education technology and publishing companies it might acquire, and plans to move to listing on Nasdaq from the OTC market.