The incident happened at a home on the 2900 block of Rio Verde.
The three-year-old girl was playing in the back yard Tuesday evening. The snake was apparently hiding in some weeds when it bit the child.
The parents called 911 about an allergic reaction and told crews they thought it was a snake bite.
She was apparently bit in the foot.
The child was airlifted to the hospital along with the snake that emergency responders captured and placed into a jar.
"Out here, we live in an area where we're up against nature all the time," said Josh Andrews of the Contra Costa County Fire Protection District. "So when it starts to warm up and those animals start to come out, we want to be sure we've cleared the weeds away from our house, for the fire danger and those animals. Especially snakes at this time of year."
No word yet on how the little girl is doing.