TALUS SLOPE:
or
SCREE SLOPE: 

A usually steep slope made up of broken off pieces about 3 inches in diameter of basalt or other lava flow created rock which cooled rapidly enough to cause the non-crystalline formation.

This is almost impossible to ride over on a bicycle so one must hike the bike over it.

Another funny definition is: two steps up, one step slid down.

A four hundred foot basalt talus slope would really be difficult to climb.