Final answer:
Aven's idea for Stagecoach Pass during hot summer weather was to find shelter in caves or under the shade of trees.
Step-by-step explanation:
Aven's idea for Stagecoach Pass when it got very hot during the summer was to find shelter in caves or under the shade of trees. In the passage, it mentions that Aven climbed into a shallow cave and fell asleep during the hot summer day. This shows that finding a cool and shaded spot was Aven's solution to deal with the heat.