(plaintiff was injured while sledding on mound of topsoil at defendant's park; topsoil had been excavated from construction site and dumped at park along with railroad tie and other construction material due to lack of storage space at defendant's maintenance facility; plaintiff slid down mound covered with snow and hit head on railroad tie breaking neck and rendering self paraplegic; court upheld trial court and appellate court dismissals of case on defendant's summary judgment motion on basis that state recreational use statute barred suit; character of property not changed and defendant's alleged creation of hazard immaterial; court noted that property owner owes no duty to recreational user (which plaintiff admitted he was) to keep property safe for entry or use; court noted that creating exception to that rule was domain of legislature and not the court - court stated, "we will not create an exception by judicial fiat").