The mountain climbers cached their provisions for the descent in a cave they could easily locate but that was inaccessible to animals. Toscreen is to shield or block from the view of others by interposing something such as a screen:
登山者们把下山给养品在山洞里使动物无法取得他们又容易寻找。 Screen 的意思是用屏风等物隔开从使别人看不见: