have pointed out that the angular nature of some oF the pebbles suggests that they may have been locally rleriverl, bec;iuse it is unlikely that they coulrl have been trans- paited by nvers for 650 km v;.ithaut becoming rounded

The basal sanrlstone unit consists largely of fluvial and Hoorlplain deposits, and represents a time v~hen the Golden-Mornson area v;as traversed by streanas flov~ing eastv:ard out of the hills to the v, est The presence of both dinosaur bones and possible track cross-sections in these deposits indicates that dinosauls lived ln the Brea at the tilde. tholrgll the lenlalns ale sparse. ancl the unit has not been quarried for bones

The gray and red muristone unit and the gray claystone and limestone unit consist mostly of lake deposits They represent a shift in environment from an area drained by I 1 vers and stl earls to an 81 ea tl13t divas i epeatecllv lnlrn- daterl by standing ~vater in the form of perennial freshv a- ter lakes At times, the lakes rlried up and ~ere replaced by floodplains In his regional study of lacustnne deposits of the i%4ofl ison Formation ln east-centlal Cololaclo, Duna- gan (1998) noted the presence of both open-lacustrine and nurginal-lacustrine deposit~ The lake deposits at the I-70 anrl Alameda Park>,'ay roadcuts are composecl of marginal lacustrine deposits, indicating that the Golden-Morrison area divas repeatedly a shoreline area during deposition of these units The presence of fossil green algae and the near lack of organic-rich laminated shales in the open- lacUstrine deposits ll'Bplies that the lakes vrere shallow and riid not have a permanently stratifierl v;ater column like some of the Green River lakes (Ryder et al, 1976) Oxidiz- ing conditions prevailed, so organic naatter such as plant debiis v~as not readily preserverl These conditions have hampered our efforts to Understand v:hat the large her- blvefous dinosaurs. such 'Js ApclIQsrltl pLi$. n'light have eaten Charactenstics of the paleasols in the Morrison For- mation have led Retallack (1997) to suggest that apen far- est vegetation (lycapacls, ferns. cycads) may have pre-