Answer:

boulder

AnswerCrossword Clue
BOULDERMile-high city
BOULDERDenver neighbor
BOULDERCity near Denver.
BOULDERLarge mass of rock.
BOULDERCity just E of Front Range.
BOULDERHoover Dam's old name
BOULDERPlymouth Rock, e.g.
BOULDERCity near the world's highest dam
BOULDERObstruction at the entrance to a cave, maybe
BOULDERRock that may be hard to roll
BOULDERColorado college town
BOULDERColorado River dam (officially "Hoover")
BOULDERHeavy rock