Surface exposure dating using cosmogenic nuclides have primarily been applied to boulders and bedrock that date to the last glacial maximum and younger (< 25,000 years). Although cosmogenic nuclides have be used to measure exposure ages of millions of years in Antarctica, in more temperate regions, erosion and exhumation become increasingly likely and exposure ages more difficult to interpret. East of Lago Buenos Aries, Argentina, glacial moraines and outwash marking advances of the Patagonian ice cap are interbedded with lava flows. ⁴⁰Ar/³⁹Ar dating of the flows indicates that six moraines were deposited between 760,000 and 1 million years ago. Exposure ages of boulders on these moraines are only several hundred thousand years. This result, combined with the wide scatter in the ages, indicates that the boulders were exhumed at various times long after moraine formation. We have collected a suite of olivine basalt samples ranging from the highest existing boulders to samples barely exposed at the surface, to constrain exhumation rates (erosion of the moraine matrix) on one of these old moraines. We are also exploring the possibilities of dating the intervening outwash plains using depth profiles of cosmogenic ³He concentrations obtained from basalt cobbles in excavations. We hypothesize that erosion of these flat outwash surfaces is much less than on the adjacent moraine slopes and that exposure ages will more closely relate to formation of the deposit.