Hooper, 1938 2 mi. W Oakley, 50 ft., Contra Costa County California. June 21, Left Berkeley this morning at 10: A.M. with Dawson Feathers in my Plymouth. Drove on main hwy. to south side of Corquinez Bridge. Stopped there to look for ground squirrels. After about 45 min there drove thru Crockett to about 1 mi. E SE when and where again hunted for squirrels. Drove into Martinez, after hunting at above locality for about another hour, for lunch and food for tonight. I hence to Concord and Clayton, over Marsh Creek Road to Cherry Canyon on the south fork of Marsh Creek. Up Cherry Canyon to about 1000 ft., then back down and to main highway on north fork of Marsh Creek or Road to Byron. 5 mi. W of Byron we turned north to Brentwood, thence north and west to this locality: 2 mi. W Oakley, 50 ft., Contra Costa County, California. Here in mixed area, (1) part uncultivated and with rather thick stands of Adenostema, occasional tree oak and undergrowth with wild oats and brome? and (2) along edge of grain field I set 69 mouse traps about 10 pace apart.