This is the lot that Steve and Janet go to when picking out a Christmas tree for Maddy, and they run into Janet's parents in the season 10 episode "Nine Yolks Whipped Lightly".
Van Nuys - Sherman Oaks War Memorial Park. Corner of Hartsook St and Van Nuys Blvd, Van Nuys CA
Note: This is the same park where Brandon gets discovered for TV while rollerblading in Season 1