in ▁among ▁many ▁located ▁in ▁close ▁proxim ity ▁to ▁each ▁other ▁in ▁the ▁valle ys ▁of ▁the ▁Cas ma ▁and ▁Se chin ▁R ivers . ▁ ▁In ▁ 2 0 0 8 , ▁a ▁German ▁and ▁Per uv ian ▁arch ae ological ▁team , ▁head ed ▁by ▁Peter ▁F uchs , ▁announced ▁that ▁a ▁circular ▁pla za , ▁ ▁in ▁diameter ▁and ▁constructed ▁of ▁rocks ▁and ▁rect angular ▁ad obe ▁br icks ▁had ▁been ▁found ▁at ▁Se chin ▁B ajo . ▁Rad i oc ar bon ▁d ating ▁indicated ▁that ▁pla za ▁was ▁constructed ▁in ▁ 3 5 0 0 ▁BC . ▁A ▁nearby ▁ 2 ▁meter - t all ▁( 2 ▁yards ) ▁fr ie ze ▁was ▁dated ▁at ▁ 3 6 0 0 ▁BC . ▁The ▁pla za ▁and ▁the ▁fr ie ze ▁are ▁the ▁two ▁oldest ▁examples ▁of ▁monument al ▁architecture ▁discovered ▁thus ▁far ▁in ▁the ▁Amer icas . ▁Se chin ▁B ajo ▁may ▁cont end ▁with ▁sites ▁of ▁Norte ▁Ch ico ▁as ▁the ▁oldest ▁urban ▁settlement ▁of ▁the ▁Amer icas . ▁ ▁Environment ▁The ▁Per uv ian ▁Pacific ▁coast ▁is ▁one ▁of ▁the ▁dri est ▁desert s ▁in ▁the ▁world ▁with ▁average ▁annual ▁precip itation ▁of ▁less ▁than ▁. ▁Al ong ▁the ▁ ▁of ▁Per uv ian ▁coast , ▁ 5 7 ▁small ▁rivers ▁flow ▁into ▁the ▁sea , ▁water ed ▁by ▁the ▁higher ▁precip itation ▁received ▁in ▁the ▁And es ▁Mountains ▁in land ▁at ▁elev ations ▁higher ▁than ▁. ▁Each ▁river ▁valley ▁forms ▁a ▁linear ▁o asis ▁in