Environmental activists plan to block work crews from clearing 179 oak and sycamore trees, north of Arcadia. Bob Spencer, spokesman for the Los Angeles County Department of Public Works, confirmed that construction would begin this morning to clear the 11 acres of trees, to make room for an estimated 500 cubic yards of sediment from Santa Anita Dam, as well as debris from seven other area catch basins. Spencer said, "The purpose behind this project is public safety; the damn built in 1927 does not meet seismic standards. Arcadia city manager Don Penman hopes that the several hundred thousand cubic yards of extra capacity is not an invitation for frequent trucking from other basins.