Forty-two mature marijuana plants growing in plain view on a Chileno Valley ranch were eradicated Friday after a report of a physical altercation drew Marin County sheriff’s deputies to the property, where they inadvertently stumbled on the pot farm. The residents of the Silva dairy, located on Tomales-Petaluma Road at the intersection of Chileno Valley Road, denied any knowledge of the illegal crop, said Lt. Doug Pittman, the Point Reyes station commander, though one family member was overheard asking, “How are we going to pay the electric bill now?” The four to five-foot tall plants would have yielded about half a pound of dried marijuana each, said Karl Nichols, a spokesperson for the San Francisco division of the Drug Enforcement Agency. On the streets, he said, a pound sells for $1,500 to $2,500, meaning the Silva ranch yield could have topped $50,000. Small growing operations have become increasingly prevalent in the last five years as attitudes toward medicinal and recreational marijuana use have changed, Mr. Nichols said, resulting in lower street prices. “People know they can make money from it,” Mr. Nichols added. “There is a relatively low risk of arrest or prosecution.” Since no one claimed the plants at the Silva ranch, the property owners will face no charges.