I, or another licensed architect, could develop a site plan that meets the requirements of local authorities. I am surprised that your California jurisdiction can’t provide an accurate plat map of your property, though.
Municipalities, counties, or voting districts often make such information available at little or no cost to taxpaying residents. A scaled plat of your site will show the overall lot with property lines (including dimensions and declination), improvements such as buildings, freestanding walls or fences, natural features such as streams or lakes, significant forestry stands, Rights-of-Way, legal easements, etc. It may also indicate building restriction lines or setback requirements, but this information is usually provided only in surveys. None of the info on the plat will offer slope or grading data, however.
An accurate survey is required to obtain topographical data, but, it may be possible to get the contours from Google Earth or other sources. Assuming that professional assistance is being eschewed, I suggest you ask the local code and permit review office to locate and provide the relevant property plat information and then inquire as to where any publicly available topo data can be had.
I have experienced some success in developing site plans with such survey oriented declinations using SU alone.