Complex sentence: The group endured great logistical difficulties and physical hardships (including the loss of a plane), and on reaching Mount Marjorie (now Mount Leisler), Lasseter declared that they were, in fact, 150 miles too far north of the search zone.
Split into simpler sentences: The group endured logistical difficulties and physical hardships (including the loss of a plane). On reaching Mount Marjorie (now Mount Leisler), Lasseter declared that they were too far north of the search zone.