Due to pressure from the rising of the Rocky Mountains in southwestern Alberta, 80 to 55 million years ago, the oil was driven northeast hundreds of kilometres and trapped into underground sand deposits left behind by ancient river beds and ocean beaches, thus forming the oil sands.
dˈuː tə pɹˈɛʃɚ fɹʌmðə ɹˈaɪzɪŋ ʌvðə ɹˈɑːki mˈaʊntɪnz ɪn saʊθwˈɛstɚn ælbˈɜːɾə, ˈeɪɾi tə fˈɪfti fˈaɪv mˈɪliən jˈɪɹz ɐɡˈoʊ, ðɪ ˈɔɪl wʌz dɹˈɪvən nˈɔːɹθiːst hˈʌndɹɪdz ʌv kˈɪləmˌiːɾɚz ænd tɹˈæpt ˌɪntʊ ˌʌndɚɡɹˈaʊnd sˈænd dᵻpˈɑːzɪts lˈɛft bᵻhˌaɪnd baɪ ˈeɪntʃənt ɹˈɪvɚ bˈɛdz ænd ˈoʊʃən bˈiːtʃᵻz, ðˈʌs fˈɔːɹmɪŋ ðɪ ˈɔɪl sˈændz.